[FTR] split configs by target into multiple manifest files (#187440)

## Summary

Part of #186515

Split FTR configs manifest into multiple files based on distro
(serverless/stateful) and area of testing (platform/solutions)
Update the CI scripts to support the change, but without logic
modification

More context:

With this change we will have a clear split of FTR test configs owned by
Platform and Solutions. It is a starting point to make configs
discoverable, our test pipelines be flexible and run tests based on
distro/solution.

.buildkite/ftr_base_serverless_configs.yml

@@ -0,0 +1,7 @@
+disabled:
+  # Base config files, only necessary to inform config finding script
+
+  # Serverless base config files
+  - x-pack/test_serverless/api_integration/config.base.ts
+  - x-pack/test_serverless/functional/config.base.ts
+  - x-pack/test_serverless/shared/config.base.ts

.buildkite/ftr_configs_manifests.json

@@ -0,0 +1,14 @@
+{
+    "stateful": [
+        ".buildkite/ftr_platform_stateful_configs.yml",
+        ".buildkite/ftr_oblt_stateful_configs.yml",
+        ".buildkite/ftr_security_stateful_configs.yml",
+        ".buildkite/ftr_search_stateful_configs.yml"
+    ],
+    "serverless" : [
+        ".buildkite/ftr_base_serverless_configs.yml",
+        ".buildkite/ftr_oblt_serverless_configs.yml",
+        ".buildkite/ftr_security_serverless_configs.yml",
+        ".buildkite/ftr_search_serverless_configs.yml"
+    ]
+}

.buildkite/ftr_oblt_serverless_configs.yml

@@ -0,0 +1,27 @@
+disabled:
+  # Base config files, only necessary to inform config finding script
+
+  # Cypress configs, for now these are still run manually
+  - x-pack/test_serverless/functional/test_suites/observability/cypress/config_headless.ts
+  - x-pack/test_serverless/functional/test_suites/observability/cypress/config_runner.ts
+
+  # Serverless feature flag config files (move to enabled after tests are added)
+  - x-pack/test_serverless/functional/test_suites/observability/config.feature_flags.ts
+
+defaultQueue: 'n2-4-spot'
+enabled:
+  - x-pack/test_serverless/api_integration/test_suites/observability/config.ts
+  - x-pack/test_serverless/api_integration/test_suites/observability/config.feature_flags.ts
+  - x-pack/test_serverless/api_integration/test_suites/observability/common_configs/config.group1.ts
+  - x-pack/test_serverless/api_integration/test_suites/observability/fleet/config.ts
+  - x-pack/test_serverless/functional/test_suites/observability/config.ts
+  - x-pack/test_serverless/functional/test_suites/observability/config.examples.ts
+  - x-pack/test_serverless/functional/test_suites/observability/config.saved_objects_management.ts
+  - x-pack/test_serverless/functional/test_suites/observability/config.context_awareness.ts
+  - x-pack/test_serverless/functional/test_suites/observability/common_configs/config.group1.ts
+  - x-pack/test_serverless/functional/test_suites/observability/common_configs/config.group2.ts
+  - x-pack/test_serverless/functional/test_suites/observability/common_configs/config.group3.ts
+  - x-pack/test_serverless/functional/test_suites/observability/common_configs/config.group4.ts
+  - x-pack/test_serverless/functional/test_suites/observability/common_configs/config.group5.ts
+  - x-pack/test_serverless/functional/test_suites/observability/common_configs/config.group6.ts
+  - x-pack/test_serverless/functional/test_suites/observability/config.screenshots.ts

.buildkite/ftr_oblt_stateful_configs.yml

@@ -0,0 +1,44 @@
+disabled:
+  # Cypress configs, for now these are still run manually
+  - x-pack/plugins/observability_solution/observability_onboarding/e2e/ftr_config_open.ts
+  - x-pack/plugins/observability_solution/observability_onboarding/e2e/ftr_config_runner.ts
+  - x-pack/plugins/observability_solution/observability_onboarding/e2e/ftr_config.ts
+  - x-pack/plugins/observability_solution/apm/ftr_e2e/ftr_config_open.ts
+  - x-pack/plugins/observability_solution/apm/ftr_e2e/ftr_config_run.ts
+  - x-pack/plugins/observability_solution/apm/ftr_e2e/ftr_config.ts
+  - x-pack/plugins/observability_solution/profiling/e2e/ftr_config_open.ts
+  - x-pack/plugins/observability_solution/profiling/e2e/ftr_config_runner.ts
+  - x-pack/plugins/observability_solution/profiling/e2e/ftr_config.ts
+
+  # Elastic Synthetics configs
+  - x-pack/plugins/observability_solution/uptime/e2e/uptime/synthetics_run.ts
+  - x-pack/plugins/observability_solution/synthetics/e2e/config.ts
+  - x-pack/plugins/observability_solution/synthetics/e2e/synthetics/synthetics_run.ts
+  - x-pack/plugins/observability_solution/exploratory_view/e2e/synthetics_run.ts
+  - x-pack/plugins/observability_solution/ux/e2e/synthetics_run.ts
+  - x-pack/plugins/observability_solution/slo/e2e/synthetics_run.ts
+
+defaultQueue: 'n2-4-spot'
+enabled:
+  - x-pack/test/alerting_api_integration/observability/config.ts
+  - x-pack/test/api_integration/apis/logs_ui/config.ts
+  - x-pack/test/api_integration/apis/metrics_ui/config.ts
+  - x-pack/test/api_integration/apis/osquery/config.ts
+  - x-pack/test/api_integration/apis/synthetics/config.ts
+  - x-pack/test/api_integration/apis/slos/config.ts
+  - x-pack/test/api_integration/apis/uptime/config.ts
+  - x-pack/test/dataset_quality_api_integration/basic/config.ts
+  - x-pack/test/functional/apps/observability_logs_explorer/config.ts
+  - x-pack/test/functional/apps/dataset_quality/config.ts
+  - x-pack/test/functional/apps/slo/embeddables/config.ts
+  - x-pack/test/functional/apps/uptime/config.ts
+  - x-pack/test/observability_api_integration/basic/config.ts
+  - x-pack/test/observability_api_integration/trial/config.ts
+  - x-pack/test/observability_functional/with_rac_write.config.ts
+  - x-pack/test/observability_onboarding_api_integration/basic/config.ts
+  - x-pack/test/observability_onboarding_api_integration/cloud/config.ts
+  - x-pack/test/observability_ai_assistant_api_integration/enterprise/config.ts
+  - x-pack/test/observability_ai_assistant_functional/enterprise/config.ts
+  - x-pack/test/profiling_api_integration/cloud/config.ts
+  - x-pack/test/functional/apps/apm/config.ts
+