Refactor app/pkg init logic

[100mik]

What this PR does / why we need it:

Refactors and cleans up app/package init logic

Which issue(s) this PR fixes:

Fixes #827

Does this PR introduce a user-facing change?

NONE

Review Checklist:

• [ ] Follows the developer guidelines
• [ ] Relevant tests are added or updated
• [ ] Relevant docs in this repo added or updated
• [ ] Relevant carvel.dev docs added or updated in a separate PR and there's a link to that PR
• [ ] Code is at least as readable and maintainable as it was before this change

Additional documentation e.g., Proposal, usage docs, etc.:

[100mik]

Gotta work towards wrapping up pending cleanup on this through a bunch of reviews @praveenrewar