[8.15] Edit related_integrations field for custom rules in UI [classic] (backport #5151)

[mergify]

Important

Do not merge to main until after 8.14.0 release, maybe until 8.15 feature freeze. This is to avoid adding 8.15 features into previous versions' branches (since those branches would be cut from main).

Contributes to #5099 by adding a step for Related integrations in the rule creation docs.

Preview

Create a detection rule

Twin PR for serverless

• https://github.com/elastic/staging-serverless-security-docs/pull/337

Related

• I'm expecting a conflict between this PR and Edit required_fields field for custom rules in UI [classic] #5287, since both PRs change the same lines in the same file. Will need to resolve by including both steps in the correct order that they appear in the UI (first Required fields, then Related integrations).

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  This is an automatic backport of pull request Edit related_integrations field for custom rules in UI [classic] #5151 done by Mergify.

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