CLI - changes command

[cdhanna]

I would love to have a beam changes command suite that would let us inspect changelogs across the beamable product lanes.... Our "source-of-truth" from changelogs are on a public github repo that we can read, so we could do stuff like,

beam changes show --version 1.19.20 --products cli #prints out changes for the cli's 1.19.20 release header
beam changes diff --version-range 1.14,1.19.19 --products unity-sdk #prints the changes between the given range
beam changes preview #alias for diff --version-range <current-version>,<latest-version> --products cli, aka, prints out the changes that are available to your CLI, but aren't installed

beam changes history # shows the last 5 versions of the changelog
beam changes open # opens the changes website

Part of this work needs to be changing the release flow to take advantage of this command, so it doesn't wither and die.

[allister-beamable]

Ideas for switches:

• --since x.y.z
• --until x.y.z (if you supply since and until, and since is after until, print a warning that since needs to be before until)

[cdhanna]

the beam changes open is super low hanging fruit.

[allister-beamable]

From Git, I am used to git log -n 3 to see the last 3 revisions. Not sure whether we want to mimic Git too closely, but it is a decent reference point for what keyboard warriors are used to.

[cdhanna]

this would be useful for creating the Release body of the Github Release pages