add pod annotations to digger-backend helm chart

[windrammer]

This PR will add the possibility to set pod annotations in the backend deployment.

✅ AI Disclosure Checklist

• I understand that all AI assistance must be disclosed.
• I did not use AI tools in this contribution.
• I used AI tools and have disclosed details below.

Details:
Github copilot gpt-4.1 used for autocompletion
I know that doesn't require disclosure but with such a small PR i figure I might as well.

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💡 Notes

• Trivial auto-completions (single words, short phrases) don’t need disclosure.
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[asosso]

Hi @windrammer,

I also need to add some annotations to the pod. Could you update the PR to the new helm-chart location? https://github.com/diggerhq/digger/tree/develop/self-hosting/kubernetes/helm-charts/digger-backend

Thank you

[windrammer]

I have moved on to other things in the months since I opened this PR. It's probably easier to create a new fork and PR with all the changes that have been made to the repo.