Move wal-g-exporter to dedicated pod (#593)

* Move wal-g-exporter to dedicated pod

* update github actions

* Remove (currently) unused reference to configMap

* Add emtpyDir for /tmp

* Add code to disable wal-g-exporter deployment

* Make image configurable

* I keep adding that...

* Refactor

* Remove backup-exporter from Service and ServiceMonitor

* Add podMonitor for wal-g-exporter

* Migrate to ptr

* Add TODO

* Rename flags for consistency

* Add additional configuration options

* Rename

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Co-authored-by: Ulrich Schreiner <[email protected]>

Author: eberlep