om init: Ready for public use

[srid]

What we need to do before om init is ready for public use:

• Non-interactive version of om init
  • Further simplify om init configuration #242
• Write a testing infra for testing initializing of various templates with various possible param config
• Identity anything the params spec should adopt or change, before we finalize it.
• Upstream the params from local registry to upstream repo, once the spec finalizes (see above point)
  • Adjust CLI to support a registry of external repos (untagged), as well as initializing specific repo. om init: Upstream params, and support arbitrary flake as argument #281

For next steps, see #282

[srid]

I'd like to consider adopting flake-schemas in this process somewhere:

https://github.com/DeterminateSystems/flake-schemas/blob/0a5c42297d870156d9c57d8f99e476b738dcd982/flake.nix#L173-L192

(In particular, perhaps om.templates can also be specified as a schema, and we can merge this with the default templates schema to get unified configuration?)

May have to wait for @shivaraj-bh 's PRs for that ...