Add Environment Variable To Helm Chart To Check Usage

[jonathanrainer]

Add an Environment variable to the container that's deployed so that we can easily scan if customers are deploying using the official Helm Chart or some other way.

Ran this through the templater and it generates correctly so there's little to test beyond that.

Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• [x] Changes are compatible[^1]
• [x] Documentation[^2] completed
• [x] Performance impact assessed and acceptable
• Tests added and passing[^3]
  • [x] Unit Tests
  • [x] Integration Tests
  • [x] Manual Tests

Notes

[^1]: It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. [^2]: Configuration is an important part of many changes. Where applicable please try to document configuration examples. [^3]: Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions.

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