Add konnect.entityID to allow adopting existing entities from Konnect

[randmonkey]

Problem Statement

From Kong/gateway-operator#460 to adopt existing entities in Konnect.
We should define a spec.konnect.entityID to enable users to adopt an existing entity in Konnect with the specified ID. Based on the field, we should also define validation rules (present only controlled by Konnect Entity controller; immutable after progammed; ...).

Proposed Solution

Define a KonnectAttributes type including the EntityID field, and add the field in the spec of all CRDs supported in the Konnect entity controller.
Also we need to add at least the following rules on the field:

• Can only be present when its controlPlaneRef is pointing to a Konnect Control plane
• Be immutable when the resource is "Programmed", which means that the resource is already associated with a Konnect entity

Additional Information

Acceptance Criteria

• konnect.entityID is present in each CRD we support in Konnect entity controller
• Have the validation rules (CELs) to check the field
  • Can only be present when its controlPlaneRef is pointing to a Konnect Control plane
  • Cannot be added, modified or unset when the resource is "Programmed" (pointing to a Konnect entity)

[pmalek]

konnect.entityID might be a bit ambiguous: users might take it as "when creating this resource, set this ID".

How about:

spec:
  konnect:
    adopt:
      by: id # to allow interface extension in the future 
      id: <id_to_adopt>

or

spec:
  konnect:
    adoptId: <id_to_adopt>

WDYT?

[randmonkey]

I think the former one

spec:
  konnect:
    adopt:
      by: id # to allow interface extension in the future 
      id: <id_to_adopt>

would make more sense, since @czeslavo has some thoughts of options of not changing the Konnect entity when it is not the same as the spec. This provides room for extensions.

[czeslavo]

How about making the strategy a parameter so it's clear what will be the behavior?

spec:
  konnect:
    adoption: # to use nouns instead of verbs
      strategy: OverrideKonnectConfig # possible alternatives could be 'HaltOnKonnectConfigMismatch' or 'AdoptKonnectConfig'
      id: <id_to_adopt>

[pmalek]

Looks good for me 👍

I'm not sure about the usability of AdoptKonnectConfig strategy there (but that's a separate discussion I reckon).

[czeslavo]

Generally, I think we should hold on with merging this API until we reach a consensus in the design doc.

[lahabana]

Current decision is that this is no longer required for kgo 1.5