Update dockerfile

[ajkyffin]

• Merge main
• Split into a build stage and an install/run stage
• Use the python:alpine base image
• Run as a non-root user
• Generate JWT keys in the entrypoint script instead of saving them in the image

[codecov[bot]]

Codecov Report

Base: 65.55% // Head: 65.55% // No change to project coverage :thumbsup:

Coverage data is based on head (485156c) compared to base (327dd39). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## k8s-deployment #89 +/- ## =============================================== Coverage 65.55% 65.55% =============================================== Files 9 9 Lines 360 360 Branches 13 13 =============================================== Hits 236 236 Misses 124 124 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ral-facilities). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=ral-facilities)

:umbrella: View full report at Codecov.
:loudspeaker: Do you have feedback about the report comment? Let us know in this issue.