Cherry-pick #22213 to 7.x: Rename google-pubsub Filebeat input to gcp-pubsub

[kaiyan-sheng]

Cherry-pick of PR #22213 to 7.x branch. Original message:

What does this PR do?

This PR is to rename google-pubsub input to gcp-pubsub input. This is a part of the renaming process to change googlecloud to gcp in both Metricbeat and Filebeat.

Warning log message is also added when user is using the old input name:

2020-10-28T13:54:08.841-0600    WARN    [gcp.pubsub]    gcppubsub/input.go:79   google-pubsub input name is deprecated, please use gcp-pubsub instead   {"pubsub_project": "elastic-observability", "pubsub_topic": "my-gcp-pubsub-topic-name", "pubsub_subscription": {"Name":"my-gcp-pubsub-subscription-name","NumGoroutines":1,"MaxOutstandingMessages":1000,"Create":true}}

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

How to test this PR locally

This should not be a breaking change so both google-pubsub and gcp-pubsub input names should work.

1. Test google-pubsub name:

filebeat.inputs:
- type: google-pubsub
  enabled: true
  project_id: elastic-observability
  topic: my-gcp-pubsub-topic-name
  subscription.name: my-gcp-pubsub-subscription-name
  credentials_file: "/Users/kaiyansheng/Desktop/elastic-observability-5537b831234a.json"

1. Test gcp-pubsub name:

filebeat.inputs:
- type: gcp-pubsub
  enabled: true
  project_id: elastic-observability
  topic: my-gcp-pubsub-topic-name
  subscription.name: my-gcp-pubsub-subscription-name
  credentials_file: "/Users/kaiyansheng/Desktop/elastic-observability-5537b831234a.json"

Related issues

• Relates Fix inconsistency of GCP Filebeat/Metricbeat names #19467

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)

[elasticmachine]

Pinging @elastic/ingest-management (Team:Ingest Management)

[elasticmachine]

💚 Flaky test report

Tests succeeded.

Expand to view the summary

Test stats 🧪

Test	Results
Failed	0
Passed	5856
Skipped	573
Total	6429

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Build Cause: [Pull request #22499 opened]

• Start Time: 2020-11-09T18:18:53.438+0000

• Duration: 55 min 20 sec

Test stats 🧪

Test	Results
Failed	0
Passed	5856
Skipped	573
Total	6429

[michalpristas]

change looks good