WIP: basic helm3 support as a datasource

[gotwarlost]

Implements a custom helm3 data source and provides examples of use, using a pattern that keeps all helm3 values and configuration in one place with the exception of the computed var entry that is needed in qbec.yaml. This is as close as I can get without having a bunch of unrelated files in random places each of which contributes to the final result.

The victoria-metrics component does not work because I think it needs some good values to be set. It shows you what happens on an error though.

$ # checkout this branch
$ cd examples/helm3
$ qbec show default -c apache # works
$ qbec show default -c victoria-metrics # prints multiple pages of errors right now

[codecov-commenter]

Codecov Report

Merging #265 (d0407db) into main (2ae1106) will decrease coverage by 1.45%.
The diff coverage is 19.57%.

@@            Coverage Diff             @@
##             main     #265      +/-   ##
==========================================
- Coverage   74.13%   72.68%   -1.46%     
==========================================
  Files          72       73       +1     
  Lines        6933     7121     +188     
==========================================
+ Hits         5140     5176      +36     
- Misses       1585     1737     +152     
  Partials      208      208              

Impacted Files	Coverage Δ
vm/internal/ds/factory/datasource.go	82.14% <0.00%> (-9.86%)	⬇️
vm/internal/ds/helm3/helm3.go	19.45% <19.45%> (ø)
vm/internal/ds/exec/exec.go	100.00% <100.00%> (ø)

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[gotwarlost]

@Andor @kvaps - any feedback?

[Andor]

Sorry, I did not try it yet and not sure will I have time to test it in the near future.