[mdatagen] allow adding resource_attribute warnings

[povilasv]

Description:

allow adding resource_attribute warnings

Link to tracking Issue: #19174
Testing:

• Generated unit tests
• Tested manually with some changes to k8sclusterreceiver:

  k8s.kubelet.version:
    description: The version of Kubelet running on the node.
    type: string
    enabled: false
    warnings:
      if_configured: This resource_attribute is deprecated and will be removed soon.

  opencensus.resourcetype:
    description: The OpenCensus resource type.
    type: string
    enabled: true
    warnings:
      if_enabled: This resource_attribute is deprecated and will be removed soon.

Gives the following output:

{"level":"warn","ts":1695985300.0413303,"caller":"metadata/generated_metrics.go:2201","msg":"[WARNING] `k8s.kubelet.version` should not be configured: This resource_attribute is deprecated and will be removed soon.","kind":"receiver","name":"k8s_cluster","data_type":"metrics"}     
{"level":"warn","ts":1695985300.041354,"caller":"metadata/generated_metrics.go:2207","msg":"[WARNING] `opencensus.resourcetype` should not be enabled: This resource_attribute is deprecated and will be removed soon.","kind":"receiver","name":"k8s_cluster","data_type":"metrics"}

Documentation:

[povilasv]

👋 FYI this PR changes generated ResourceAttributeConfig for a lot of receivers and processors.
It adds an internal field enabledSetByUser, so we can detect when user manually enabled resource attribute (vs enabled by default).

Example of change:

	enabledSetByUser bool
}

func (rac *ResourceAttributeConfig) Unmarshal(parser *confmap.Conf) error {
	if parser == nil {
		return nil
	}
	err := parser.Unmarshal(rac, confmap.WithErrorUnused())
	if err != nil {
		return err
	}
	rac.enabledSetByUser = parser.IsSet("enabled")
	return nil
}

I had to update some receiver tests so that it ignores this internal field

[dmitryax]

Thanks @povilasv!