fix: Accept jmx config as object or array

[lorespiz]

Description of changes: Added a custom UnmarshalJSON on the jmx marker struct in internal/manifests/collector/adapters/config_from.go that accepts both a single object or an array and returns an error for any other type.
The field remains a *jmx pointer, so all existing presence checks (e.g. in ports.go and controllers/common.go) work unchanged; no call sites needed modification.

Testing:

• Added unit testing TestConfigStructFromJSONString.
• Manual E2E test on EKS cluster:
  • Built the operator image from this branch and deployed it via make deploy
  • Applied an AmazonCloudWatchAgent CR (daemonset mode) with jmx configured as a two-element array
  • Verified: cloudwatch-agent and cloudwatch-agent-headless Services are created with port 4314/TCP, persist across reconciles, and no config-parsing errors appear in the operator logs

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.