Add support for mapping APIKey manifests into secrets

[K-Phoen]

Needs K-Phoen/grabana#161 + some tests

[codecov-commenter]

Codecov Report

Merging #110 (0554cf8) into master (642d965) will decrease coverage by 5.53%.
The diff coverage is 0.81%.

@@            Coverage Diff             @@
##           master     #110      +/-   ##
==========================================
- Coverage   47.46%   41.93%   -5.54%     
==========================================
  Files          27       31       +4     
  Lines        1616     1834     +218     
==========================================
+ Hits          767      769       +2     
- Misses        824     1040     +216     
  Partials       25       25              

Impacted Files	Coverage Δ
internal/pkg/controllers/apikey_controller.go	0.00% <0.00%> (ø)
internal/pkg/controllers/datasource_controller.go	0.00% <0.00%> (ø)
internal/pkg/grafana/apikeys.go	0.00% <0.00%> (ø)
internal/pkg/kubernetes/secrets.go	0.00% <0.00%> (ø)
internal/pkg/kubernetes/valueref.go	0.00% <0.00%> (ø)
api/v1alpha1/apikey_types.go	100.00% <100.00%> (ø)