[8.12] Document how to query for a specific feature within rank_features (#110749)

[ioanatia]

Backports the following commits to 8.12:

• Document how to query for a specific feature within rank_features (Document how to query for a specific feature within rank_features #110749)

[github-actions]

Documentation preview:

• ✨ Changed pages

[ioanatia]

@elasticmachine test this please

[leemthompo]

@elasticmachine test this

[leemthompo]

Important

Elastic documentation is migrating to Markdown for version 9.0+. See the migration guide for details.

ℹ️ What's happening?

• Starting January 29, we will start closing all unmerged documentation PRs targeting main/master
• We're migrating from AsciiDoc to Markdown for 9.0+
• 9.0 docs will be frozen from January 29 until February 20 2024
• NOTE: PRs that include both code and documentation changes will remain open

What do I need to do?

For <=8.x docs:

1. Rebase your PR to target the relevant 8.x branch instead
2. The content can remain in AsciiDoc format

For 9.0+ docs:

Option 1:

• Draft docs in Markdown
• Once migration freeze ends, find the relevant page in the new docs system and use the edit options to submit your changes

Option 2:

• Open an issue in elastic/docs-content

💡 Need help?

1. For Elasticians: Ask in #docs Slack channel
2. For external contributors: Open an issue in elastic/docs-content