Help users diagnose indexing issues

[andyw8]

We've had couple of recent issues relating to indexing:

#2287
#2295

To aid with troubleshooting, we could add a section in the docs and link to it from that error. The docs can explain how to use ruby-lsp-doctor, and how to temporarily ignore problematic gems/files.

[st0012]

1. Make ruby-lsp-doctor a flag of ruby-lsp instead to improve discoverability
2. Move the exception rescue inside @global_state.index.index_all so we can provide more information about the failed indexing action

[andyw8]

Note: The ruby-lsp-doctor command is now ruby-lsp --doctor (#2310)

[github-actions]

This issue is being marked as stale because there was no activity in the last 2 months