Notify of new major versions available when running gleam update

[lpil]

Discussed in #3841

^{Originally posted by hayleigh-dot-dev November 17, 2024}
As the ecosystem grows it is becoming more difficult to keep track of when packages are updated with new breaking changes. Short of just making a list of every dependency of every package I maintain and regularly checking for new versions, there is no real way to know if any of my dependencies have updated until a user opens an issue or I notice by happenstance.

One thing I can do reliably is run gleam update in my packages from time to time. I'd like to propose that command also reports when any major version bumps are available, something like:

 % gleam deps update
  Resolving versions
Downloading packages
 Downloaded 2 packages in 0.01s
 
Hint: the following dependencies have new major versions available...

- wibble@2
- wobble@3

I think this would have a general benefit to the community:

• package consumers get notified when things have moved on and can make an informed decision to upgrade or not.
• package authors have an easier time broadcasting new changes, which is particularly impactful for "foundation" packages like mist or lustre where the community at large benefits from being on the same version.
• package authors can more-easily make sure they're not fragmenting the community by sticking on old versions of dependencies unnecessarily.

[lpil]

Let's do it. I think Mix and Cargo have a nice way of displaying this