Extract indexer resync procedure into standalone page

[linconvidal]

Context

The How to Resynchronize the Indexer procedure currently lives inside the Pruning documentation page, but it's needed in other contexts too (e.g., major version upgrades, schema migrations, unparsed block recovery).

Requested changes

1. Extract the "How to Resynchronize the Indexer" section from docs/advanced-configuration/pruning.md into its own standalone page (e.g., docs/advanced-configuration/resync-indexer.md).
2. Update the search_path reference in that section — it still defaults to mainnet, but since v2.0.0 the schema is public (DB_SCHEMA=public).
3. Add cross-links from the pruning page and the unparsed blocks page to the new standalone page.

Why

• Release notes for v2.0.0 and v2.1.0 need to link to a resync procedure that isn't specific to pruning.
• The outdated search_path default (mainnet instead of public) could confuse users upgrading to v2.x.