Add index routing

[chaitanyaphalak]

Use splunk.com/index annotation on pod and/or namespace to tell which Splunk platform indexes to ingest to.

Pod annotation will take precedence over namespace annotation when both are annotated.

Docs will be merged from https://github.com/splunk/sck-otel

[dmitryax]

LGTM. Please run make render or install pre-commit hook

[dmitryax]

Thanks!