Feature Enabling and Disabling of jaeger-agent

[Mactherobot]

Due to deprecation of the jaeger agent, and the fact that jaeger can accept the traces directly via OTEL SDK. I don't know if this change is too simple and will introduce side effects. So please help me, if i'm missing anything.

Which problem is this PR solving?

• Resolves: #2322

Description of the changes

• Adds the enabled flag for the jaegerAgentSpec
• Returns nil if the value is not defined or set to false.

How was this change tested?

• By unit tests

Checklist

• [X] I have read https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
• [X] I have signed all commits
• [X] I have added unit tests for the new functionality
• [X] I have run lint and test steps successfully
  • for jaeger: make lint test
  • for jaeger-ui: yarn lint and yarn test

[iblancasa]

You need to regenerate the bundle to make the CI pass.