[ResponseOps][Stack Connectors] Add helptext for Opsgenie connector

[lcawl]

Summary

Relates to #142776

This PR adds help text to the UI fields related to testing the OpsGenie connector, based on some descriptions of the fields in https://support.atlassian.com/opsgenie/docs/alert-fields/

Checklist

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support

Screenshots

Before

Create alert:

Close alert:

After

Create alert:

Close alert:

[elasticmachine]

Pinging @elastic/response-ops (Team:ResponseOps)

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 01c88ec

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
stackConnectors	411.6KB	414.4KB	+2.7KB

Unknown metric groups

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
fleet	59	65	+6
osquery	108	113	+5
securitySolution	441	447	+6
total			+19

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
fleet	67	73	+6
osquery	109	115	+6
securitySolution	518	524	+6
total			+20

History

• 💔 Build #87826 failed 51d5f27
• 💔 Build #87815 failed 31c9fe0

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[jonathan-buttner]

Changes look good! Thanks Lisa.