Add tridentImageRegistry to Helm chart (trident-image-registry to cli)

[mayrstefan]

Change description

The helm chart has a parameter imageRegistry which is used to set an alternative registry url for trident and csi sidecar images which can cause an issue for some installations. That registry has to contain images from two different sources. This change keeps imageRegistry for the csi sidecar images and adds tridentImageRegistry to use for mirrored trident images. It tries to do the same for the cli with an addition trident-image-registry parameter

Project tracking

Should fix #772

Do any added TODOs have an issue in the backlog?

N/A

Did you add unit tests? Why not?

I did not find tests for imageRegistry that I could have modified and extended. But I guess it would be good to have test coverage for both parameters.

Does this code need functional testing?

Yes, because I'm no programmer and I don't know if I broke something I did not intend to.

Is a code review walkthrough needed? why or why not?

Don't know.

Should additional test coverage be executed in addition to pre-merge?

Don't know.

Does this code need a note in the changelog?

Changelog entry is included in this PR.

Does this code require documentation changes?

Yes. Both parameters need some documentation. ~~There is also a breaking change: imageRegistry is not used for trident images any more~~

Additional Information

None