[DOCS] Add docker-verify-signature anchor to Docker docs

[jrodewig]

Problem:

Other Elastic doc sets (Beats, APM) link to the Verify the Elasticsearch Docker image signature section of the Docker docs. This section was removed as part of #99371. When we bump to the next version, this will create broken links and break the docs build.

Solution:
Re-add the anchor so we don't create broken links or break the docs build.

This commit was added to the backports of #99371:

• [8.10] [DOCS] Streamline Docker Compose docs (#99371) #99429
• [8.9] [DOCS] Streamline Docker Compose docs (#99371) #99430

[github-actions]

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[elasticsearchmachine]

Pinging @elastic/es-docs (Team:Docs)