Refactor the helm and OCI chart clients and respective fakes.

[absoludity]

Description of the change

This is purely renaming and refactoring that I found myself wanting to do while trying to write tests for the CreateInstalledPackage endpoint of the helm plugin for the kubeapps apis server.

The renaming is from Resolver -> ChartClient , and the refactoring is to move the fakes for chart client and the chart client factory into the one file, rather than being spread out in different places.

Benefits

Clearer what the structs and interfaces are for. Enables me to continue writing tests happily :)

Possible drawbacks

None that I can see.

Applicable issues

• ref Implement further direct helm plugin features #3146

Additional information

[antgamdia]

Awesome, nice refactor, much clearer now what is each function/struct for!

Out of the scope of this PR, but wanted to say anyway :P What annoys me the most is still having the helm3to2 and the converters...
I wish we had time to clean up the /pkg folder someday

Well, indeed I started when I upgraded some go deps, but have to wait until helm 3.7 is released (this week perhaps?) because of some conflicts with the ORAS pkgs for managing OCI

[absoludity]

Awesome, nice refactor, much clearer now what is each function/struct for!

Out of the scope of this PR, but wanted to say anyway :P What annoys me the most is still having the helm3to2 and the converters...

Yeah, there's quite a few pieces of tech-debt like that which will only get removed if we happen to touch the related code and can clean it up as a fly-by (like I've done here for this stuff). Or if it annoys us so much we can't stand it any longer...

I wish we had time to clean up the /pkg folder someday

Well, indeed I started when I upgraded some go deps, but have to wait until helm 3.7 is released (this week perhaps?) because of some conflicts with the ORAS pkgs for managing OCI

Sounds like it annoyed you too much :P, great if we can remove it once 3.7 is out.