metrics: add indexer_tip metrics#4982

[eval-exec]

What problem does this PR solve?

cherry-pick https://github.com/nervosnetwork/ckb/pull/4982

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code ci-runs-only: [ quick_checks,linters ]

Side effects

• None

Release note

Title Only: Include only the PR title in the release note.