feat: Support for correlations on datasources

[majiayu000]

Fixes #2201

Summary

Adds support for configuring datasource correlations as code using the operator.

Changes

• Add correlations field to GrafanaDatasourceSpec
• Add GrafanaDatasourceCorrelation, GrafanaDatasourceCorrelationConfig, and GrafanaDatasourceCorrelationTransformation types
• Implement correlation sync in datasource controller using Grafana correlations API
• Match correlations by composite key (targetUID + label) for idempotent reconciliation
• Update CRDs and documentation

Example Usage

apiVersion: grafana.integreatly.org/v1beta1
kind: GrafanaDatasource
metadata:
  name: prometheus
spec:
  datasource:
    name: Prometheus
    type: prometheus
    url: http://prometheus:9090
  correlations:
    - targetUID: loki-uid
      label: "View in Loki"
      description: "Logs correlation"
      config:
        field: "traceID"
        target:
          expr: "{traceID=\"${__value.raw}\"}"

🤖 Generated with Claude Code

[CLAassistant]

All committers have signed the CLA.

[weisdd]

Thanks for the PR.

As with any other PR, we'd like to see tests covering the new functionality (e.g. adding, modifying, removing correlations, data conversions, etc), otherwise it'd be hard to conclude that any of those changes work as intended (manual testing is something we'd like to avoid).
For interactions with Grafana, externalGrafanaCr from controllers/suite_test.go can be re-used.

As a side note, LLMs tend to add comments everywhere, even to the blocks of code that are self-explanatory. It's better to remove those comments in places where they don't tell anything new (by new I mean, e.g., why something is implemented in a certain way). Example of a useless comment from this PR:

// Get existing correlations from Grafana
existingCorrelations, err := gClient.Datasources.GetCorrelationsBySourceUID(sourceUID)

[majiayu000]

Thanks for your reminder. Will try now!

[weisdd]

Please, don't introduce any dependencies on external services. If you need to imitate a datasource, you can use httptest.NewServer. We have a helper to sets up a mux with json content (tk8s.GetJSONmux).

[majiayu000]

@weisdd updated correlations: set Type on update requests and switched correlation tests to use a local httptest datasource URL (no external services). No tests run.

[theSuess]

It works as expected but I found some code smells I'd like to see fixed before we can merge this.

I'll defer to @weisdd or @Baarsgaard for reviewing the tests as I haven't had the time to get familiar with the recent changes to our test layout

[theSuess]

This check is not needed. We can rely upon this being non-nil if the err is nil

[theSuess]

Since this isn't a bulk API, the performance gains over the regular code path are minimal, so IMHO we can get rid of this

[theSuess]

Errors should be static in case we want to match on them at some point. Extra information like the UID/Label should go in a log entry if needed

[theSuess]

Errors should be static in case we want to match on them at some point. Extra information like the UID/Label should go in a log entry if needed

[theSuess]

No need for this to be conditional as the convertJSONToInterface can handle nil

[theSuess]

Again, no need for this to be conditional as an empty loop is skipped

[theSuess]

No need for this to be conditional as the convertJSONToInterface can handle nil

[theSuess]

Again, no need for this to be conditional as an empty loop is skipped

[majiayu000]

Thanks for the review @theSuess! I've addressed your feedback:

• Removed the dedicated deleteAllCorrelations function.
• Switched to static error messages and added logging for dynamic details.
• Simplified convertJSONToInterface and loop handling.

One note: I retained the if existingCorrelations != nil check. This is because we ignore GetCorrelationsBySourceUIDNotFound errors (setting err to nil), which results in existingCorrelations being nil. Accessing .Payload without the check would cause a panic in that specific case.