Finish spacetimedb-update functionality

[coolreader18]

Description of Changes

based off #2011

Adds implementations to all the subcommands of spacetime version.

Expected github release artifact structure:

• artifact filename: spacetime-{rustc-target-triple}.{ext}
  • ext = if windows { "zip" } else { "tar.gz" }
• artifact contents:
  • spacetimedb-cli[.exe], spacetimedb-standalone[.exe], spacetimedb-update[.exe]

cc @clockworklabs/devops - feedback on this^^ would be nice. I kept the edge cases since that's how it already was and I figured that might make it easier in the release workflow, but honestly I'd prefer if it was just spacetime-{rustc-target-triple}.{ext} if possible. Not sure where the release flow is or if it's even automated. Implemented in #2193.

Expected complexity level and risk

3 - a complex bit of code that's implementing a theoretically perpetual contract between spacetimedb-update, github release artifacts, and the directory structure.

Testing

• Manually tested that spacetime version install works
• I'm working on an automated regrtest to make sure the functionality works.
• reviewer: if you wanna, play around with it and try and catch out any edge cases?

[bfops]

(It looks like this currently isn't passing CI, so I'm holding off on review)

[bfops]

Review notes:

• The previous functionality of spacetime version is now accomplished by spacetime --version (and spacetime version list indicates which version is the current one)

[bfops]

Note to self: I still need to:

• review crates/cli/src/subcommands/version.rs
• review crates/paths
• review crates/update itself
• jot down what I think the surface area for testing is here

[coolreader18]

I removed the rm-core-as-dep-of-cli commit from this branch, I'll do it as a follow-up PR.

[bfops]

(I merged in master to bump CI. The Internal tests were failing due to them running before https://github.com/clockworklabs/SpacetimeDBPrivate/pull/1279 merged).

[bfops]

After the conversation elsewhere today, I'm approving this as-is. If we need to do further testing, changes, or code cleanups, we will have to do them in followup PRs. For now let's merge this and start getting it tested more widely.

[bfops]

(That said, CI seems to be failing)