Add LaunchBuilder

[Malax]

This PR originally started as a fix for #485. As it turns out, adding slices to Launch was already possible, albeit more complicated as it should be since there were no builder functions available for slices.

This PR adds a dedicated LaunchBuilder that allows setting all fields for Launch, removes the builder-style functions from Launch as they were inconsistent with the rest of libcnb.rs anyways. I still want to tackle #166, but this isn't the PR for that.

I also added some docs for Slice that clarify what paths actually is (and renamed it). I opted to not implement a newtype for Go standard library path globs for now as we can spend our time better in other areas. I created an issue for it as #486.

Changelog

• Replace builder style functions from Launch with a dedicated LaunchBuilder to be more consistent with other builders in the library. Additionally, all fields of Launch can now be modified via the builder pattern.
• Rename paths field in launch::Slice to path_globs and add docs to make it clearer that these strings are Go standard library globs.

Closes #485, GUS-W-11486542

[Malax]

Currently looking into a fix for the integration test failures that are triggered by us having multiple heroku/procfile buildpacks in the builder used for the integration tests. These failures are very likely not related to this PR.

Edit: Solved via 0e4279c

[edmorley]

Thank you!

[schneems]

A little late on the draw, but I reviewed this. Looks good.

I see that the slice and slices functions take something that implements Into Slice. I don't see where we're implementing that anywhere other than the default that any struct can be made into itself (though perhaps I missed it).

Do we have examples of building a slice or should we just manually create the struct for now

libcnb.rs/libcnb-data/src/launch.rs

Lines 225 to 232 in d0a35f7

	pub struct Slice {
	/// Path globs for this slice.
	///
	/// These globs need to follow the pattern syntax defined in the [Go standard library](https://golang.org/pkg/path/filepath/#Match)
	/// and only match files/directories inside the application directory.
	#[serde(rename = "paths")]
	pub path_globs: Vec<String>,
	}

?