Include exported inputs into drift event for ResourceSetInputProvider

[Mik4sa]

Fixes #850

Adds the new annotation fluxcd.controlplane.io/eventMetadataExportedInputKeys. With it the user can control which fields from exported inputs are included in the event metadata for the Flux event (alert). Optionally the name of event metadata fields can be customized.

What would it look like (for example for ResourceSetInputProvider type: OCIArtifactTag and Microsoft Teams provider):

No annotation

No behaviour change.

Annotation value: "tag,digest"

What I just realized. Here is the "digest" field missing. Is this a reserved name or so?

Annotation value: "tag=image-tag,digest=manifest-digest"

Multiple exported inputs

When there are multiple exported inputs (more than a single) then the index of the exported input is automatically added to the event metadata key:

Questions I ask myself but need feedback and guidance from you

1. Do we need a different name for the annotation than eventMetadataExportedInputKeys?
2. Do we need an addiotional annotation to enable and disable this? Like reconcile: enabled?
3. Is there anything else I haven't thought of?

Note: The code changes aren't final yet but functional complete in my eyes.

• I would add a "const" for the new annotation(s)
• Maybe there is a "better" way in retrieving the actual value from the exported input (json)
• Dropping the fallback, when the value can't be nnmarshaled from json and adding error handling instead
• Adding error handling in general

@matheuscscp maybe you can have a look at this and give me your honest opinion?

[matheuscscp]

Let's wait and see what @stefanprodan says about this when he's back next week