[DOCS] Increment headings and add anchors for CCR Docs

[jrodewig]

#45704 adds cross-cluster replication (CCR) docs to the Elasticsearch Reference Guide.

elastic/stack-docs#464 removes CCR docs from the Elastic Stack Overview.

This PR handles final cleanup for those moves, including:

• Removing :leveloffset: tags required when the docs lived in both docbooks
• Incrementing headings for CCR docs files
• Adding explicit anchors for CCR headings

Relates to #45703.

Dependencies

Don't merge this PR until the following PRs are merged:

• [DOCS] Add CCR docs to the Elasticsearch Reference Guide #45704
• [DOCS] Remove CCR docs from Stack Overview stack-docs#464

[elasticmachine]

Pinging @elastic/es-docs

[jrodewig]

This should be unneeded now that #45704 moves to a top-level chapter.