Add Implementation to provide OTEL Resource Attributes

[senthuran16]

Purpose

$Subject. Fixes wso2/api-manager#2123

Approach

OTEL Resource attributes can be provided:

• Via deployment.toml

  [[apim.open_telemetry.resource_attributes]]
  name = "service.name"
  value = "MyService"
  
  [[apim.open_telemetry.resource_attributes]]
  name = "deployment.environment"
  value = "Production"
  

AND

• Via the OTEL_RESOURCE_ATTRIBUTES environment variable (as per the OpenTelemetry spec [1])

  export OTEL_RESOURCE_ATTRIBUTES=deployment.environment=Production,service.name=MyService
  

When a resource attribute is given via both the deployment.toml and the OTEL_RESOURCE_ATTRIBUTES env variable, the value of the attribute given via the env variable will replace the value given via deployment.toml.

Related PRs

Reading the Config - j2 file change: TODO

[1] https://github.com/open-telemetry/opentelemetry-specification/blob/8946dfc6a2302f78b0224fcc3f4dfb816a7bb1f4/specification/resource/sdk.md#specifying-resource-information-via-an-environment-variable

[dushaniw]

Failing test suit has no impact from the PR changes. Hence merging. Need to separately look into the port issue in the PR build.