om ci: Support for useing & pushing to cachix

[srid]

... in addition to 'whitelist pushing' (via pins).

Basically replace this entire module via om.ci.default.<..> configuration, and have om ci take care of the rest as part its build.

omnix/nix/modules/cache-pins.nix

Lines 41 to 48 in 2aa1f48

	perSystem = { self', ... }: {
	# https://om.cachix.org will ensure that these paths are always
	# available. The rest may be be GC'ed.
	cache-pins.pathsToCache = {
	cli = self'.packages.default;
	nix-health = self'.packages.nix-health;
	};
	};

• The design should be cache agnostic, while supporting cachix to begin with (in future, we can support attic and the like).

This will obviate the following two steps in CI, in addition to the aforementioned flake-module:

omnix/.github/workflows/ci.yaml

Lines 19 to 24 in 2aa1f48

	- uses: cachix/cachix-action@v14
	if: github.ref == 'refs/heads/main'
	with:
	name: om
	authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
	skipPush: true

omnix/.github/workflows/ci.yaml

Lines 70 to 72 in 2aa1f48

	- name: Push to cachix
	if: github.ref == 'refs/heads/main'
	run: nix --option system "${{ matrix.system }}" run .#cachix-push

[srid]

Perhaps this should be decoupled and built on top of #198

[srid]

I tried to implement it only to realize that it is not that simple. Also, we don't want to complicate omnix, when the user could simply use unix tools to achieve this. For example,

$ om ci run . | rg -e "-omnix-cli-\d+\.\d+\.\d+$" -e "-omnix-mdbook-site$"
/nix/store/ppnag6lacdlg8q3vz3avv6da942ffgqw-omnix-mdbook-site
/nix/store/whdiim2js86xq14qdyk4mxfsdgni6cnh-omnix-cli-0.1.0

$ om ci run . | rg -e "-omnix-cli-\d+\.\d+\.\d+$" -e "-omnix-mdbook-site$" | xargs cachix push om

But to implement pinning (which requires naming each path to be pinned), we'll do juspay/cachix-push#6 - after which the user can simply run the following in sequence:

$ om ci run .
$ nix run .#cachix-push

Keeping cache pushes off CI is good for another reason -- it makes no sense to do that when doing local CI.

[srid]

juspay/cachix-push#7

Will document this as well.