* fix: use nodejs-lts image for building frontend code
Node v14 is end-of-life and should no longer be used. Commit changes Makefile to pull in latest node-lts instead.
Also, use local temporary folder for storing npm generated files to workaround permission issue with old npm version, e.g. emitting these errors:
```
npm ERR! code EACCES
npm ERR! syscall mkdir
npm ERR! path /.npm
npm ERR! errno -13
npm ERR!
npm ERR! Your cache folder contains root-owned files, due to a bug in
npm ERR! previous versions of npm which has since been addressed.
```
Both changes should also fix issue https://github.com/zalando/postgres-operator/issues/2651
* fix: add frontend build step
Commit d60b424d79 accidentally removed build steps that are important for building frontend.
This commit restores previous behavior, but switches to nodejs-lts image for building frontend code.
Should restore `app.js` presence in ghcr image, see https://github.com/zalando/postgres-operator/issues/2651.
* Initial commit for our basic Postgres Operator UI:
* Create and modify Postgres manifests
* Watch Operator Logs in the UI
* Observe cluster creation progress
* S3 Backup browser for clone and restore
Many thanks to Manuel Gomez and Jan Mussler for the initial UI work a long time ago!
Matthias Adler
Felix Kunde