feat(pkger): extend pkgs with source identifiers

[jsteenb2]

a good chunk of this PR is jiggling some bits to remove the high lvl Pkg from the svc interface.

references: #18243

TODOs

• add tests around different source types in Parser
• add assertions to pkger_test.go
• extend stack with sources
• ensure API is backwards compatible (when OSS beta13 is released, we can let the axe split)

• Well-formatted commit messages
• Rebased/mergeable
• Tests pass

[hoorayimhelping]

not a blocker for this, but a design consideration to have a think about:

boolean arguments trigger me hard because they provide very little context to what's happening. i assume true and false passed in to apply have to do with dry runs, but that is a wild ass guess that required looking around at the context of these calls to even have an idea. point is, boolean arguments are a kind of hard stop on comprehension and require digging into definitions to understand.

i think it's usually worth considering how the intent of this true vs false value might be captured in a way that gives context to the reader. making it an enum is one way i can think of that doesn't resort to stringly typed stuff.

[jsteenb2]

I hear you, if it were exported, I'd have addressed it. However, it's internal, and don't see it necessary here.

[hoorayimhelping]

sorry, it's hard for me to tell but is this unit tested? it seems like a prime candidate for unit tests hitting all the branches in the switch statement

[jsteenb2]

not explicitly, its an internal implementation detail. Is tested in other tests that rely on this. It is purposeful that there is very limited white box testing in pkger.