Add package-version-specific changelog to settings

[shubhbapna]

• Add a new field changelog to the per package setting
• Include a way to specify versions
• We just care about the length of the changelog (the ordering of the entries doesn't matter to us. it is on the user to maintain the ordering)

Agreed upon template:

torch:
  changelog:
    "2.3.1":
      - rebuild for xyz

[shubhbapna]

@dhellmann @tiran regarding the the template for this changelog should we have something like this if we know that one change can affect many versions:

torch:
   changelog:
        - name: rebuild xyz
          affected_versions: ["2.3.1", "2.3.2"]

or

torch:
   changelog:
        rebuild xyz:
               - "2.3.1"
               - "2.3.2"

[dhellmann]

Keeping them separate lists makes it easier to scan the list as a human reader.

How likely do you think it will be that we have an update that affects multiple versions?

[shubhbapna]

Okay, yeah the likeliness is low that it affects multiple versions at the same time (especially given that we have been trying to reduce the number of versions we build for a package in the same bootstrap)