gitSync: allow gitSync.env to take a env var from a secret reference

[connorlwilkes]

Description

Currently the schema for gitSync.env does not allow you to define env from secrets like:

env:
        - name: GIT_SYNC_USERNAME
          valueFrom:
            secretKeyRef:
              name: gitsync-secret
              key: username
        - name: GITSYNC_USERNAME
          valueFrom:
            secretKeyRef:
              name: gitsync-secret
              key: username
        - name: GIT_SYNC_PASSWORD
          valueFrom:
            secretKeyRef:
              name: gitsync-secret
              key: pwd
        - name: GITSYNC_PASSWORD
          valueFrom:
            secretKeyRef:
              name: gitsync-secret
              key: pwd

This is because the schema is overly restrictive and doesn't just reference the upstream V1EnvVar. See: https://github.com/apache/airflow/blob/main/chart/values.schema.json#L8557-L8583

Use case/motivation

No response

Related issues

https://github.com/apache/airflow/pull/39031

Are you willing to submit a PR?

• [X] Yes I am willing to submit a PR!

Code of Conduct

• [X] I agree to follow this project's Code of Conduct

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