SAMZA-2075: Add execEnvContainerId and execEnvAttemptId for diagnostics for Kubernetes job coordinator

[cameronlee314]

Issues: In YARN today, a deployment attempt id which is shared between containers for a single Samza job can be extracted from the exec-env-container-id in the diagnostics information emitted by a job. However, in other execution environments (e.g. Kubernetes), there may not be an exec-env-container-id that can be parsed to get a deployment attempt id. It isn't ideal that this attempt id must be extracted from another field.

Changes:

1. Add an explicit samza-epoch-id field to MetricsHeader which contains the id for a deployment attempt and emit this field in the diagnostics messages.
2. Update classes to accept attempt id as an argument or extract it from the SAMZA_EPOCH_ID environment variable.

Testing:

1. Updated unit tests (including compatibility tests for with and without the extra field)
2. Deployed a test job in minikube and checked the emitted diagnostics messages for the new attempt id field in the header

API changes (backwards compatible):
JSON representation of MetricsHeader (used in MetricsSnapshot) has an additional optional field called samza-epoch-id, and this field is intended to contain the deployment attempt id which is shared across all containers (job coordinator and workers) of a Samza job. This field is filled in by reading the SAMZA_EPOCH_ID environment variable.

[jia-gao]

LGTM, but someone else who has more context on this should take a look and approve

[rmatharu-zz]

lgtm