ci: handle all package documentation edits

[shmsr]

Summary

• Expand the Documentation edit helper workflow to cover all flat package source docs under packages/*/_dev/build/docs/*.md, including per-data-stream files like cloudtrail.md.
• Require both manifest.yml and changelog.yml before considering a docs package complete, and report partial metadata updates separately.
• Harden generated changelog commands by safely passing custom changelog: text between steps and shell-quoting it in the suggested command.

Test plan

• go run github.com/rhysd/actionlint/cmd/actionlint@latest .github/workflows/docs-edit-automation.yml
• Focused shell check for custom changelog: parsing with shell-sensitive text.
• Focused shell check for metadata classification: no metadata, complete metadata, missing manifest, and missing changelog.

[mrodm]

Would this pattern match packages in nested directories ?
Like packages/nginx/nginx_otel/ ?

There are still no packages located in nested directories, but it would be good that all these processes support that too to be prepared.

Related to this issue: #17403