injector: Adding unit tests for the injector package

[draychev]

This PR adds more unit test coverage for the pkg/injector

This PR also includes a rewrite of the updateAnnotation() function - to simplify and correct.
Previous iteration of this function returned add JSONPatchOperation with Value being sometimes string and other times map[string]string. The most recent iteration always creates add JSONPatchOperation with Value of map[string]string.

Before

$ go test -cover ./pkg/injector/...
ok      github.com/openservicemesh/osm/pkg/injector     0.058s  coverage: 27.6% of statements

After

$ go test -cover ./pkg/injector/...
ok      github.com/openservicemesh/osm/pkg/injector     6.821s  coverage: 75.7% of statements

---

Please mark with X for applicable areas.

• New Functionality [ ]
• Documentation [ ]
• Install [ ]
• Control Plane [ ]
• CLI Tool [ ]
• Certificate Management [ ]
• Networking [ ]
• Metrics [ ]
• SMI Policy [ ]
• Security [ ]
• Tests / CI System [X]
• Other [ ]

Please answer the following questions with yes/no.

• Does this change contain code from or inspired by another project? If so, did you notify the maintainers and provide attribution? no

[shashankram]

This PR also includes a rewrite of the updateAnnotation() function - to simplify and correct.
Previous iteration of this function returned add JSONPatchOperation with Value being sometimes string and other times map[string]string. The most recent iteration always creates add JSONPatchOperation with Value of map[string]string.

This isn't incorrect but rather as expected. The way the function works prior to this change is that if target is nil, then no annotations exist, and hence the patch value is a map, ie. a new annotation is added. If the annotation exists, then the patch no longer needs to create a new map, and only needs to update the existing object with the add map.

[shashankram]

Thanks for adding the tests, some comments regarding the existing functionality.

[codecov-io]

Codecov Report

Merging #1772 into main will increase coverage by 3.70%.
The diff coverage is 93.02%.

@@            Coverage Diff             @@
##             main    #1772      +/-   ##
==========================================
+ Coverage   55.51%   59.21%   +3.70%     
==========================================
  Files         125      125              
  Lines        5163     5171       +8     
==========================================
+ Hits         2866     3062     +196     
+ Misses       2295     2106     -189     
- Partials        2        3       +1     

Impacted Files	Coverage Δ
pkg/injector/webhook.go	73.48% <71.42%> (+39.96%)	⬆️
pkg/injector/patch.go	86.29% <97.05%> (+76.12%)	⬆️
pkg/injector/init-container.go	100.00% <100.00%> (ø)
pkg/envoy/route/config.go	95.83% <0.00%> (+0.83%)	⬆️
pkg/injector/config.go	93.91% <0.00%> (+16.52%)	⬆️
pkg/injector/volumes.go	100.00% <0.00%> (+100.00%)	⬆️

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[shashankram]

Looks correct overall, few comments and some linting issues to resolve.

[eduser25]

You know we have a mock for catalog too right? >:)