Add validations for matchers used in kapp config

**Describe the problem/challenge you have**
Currently we don't have any validations for the matchers (e.g `apiGroup` in `apiGroupKindMatcher` can have a `/`).
This causes unexpected behaviour instead of an error.

**Describe the solution you'd like**
Adding validations for these matchers would help in erroring out at an early stage instead of unexpected behaviour.
We can add the following validations:
- [ ] `apiGroup` in `apiGroupKindMatcher` shouldn't have a `/`

**Anything else you would like to add:**
[Additional information that will assist in solving the issue.]

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