Specify old version in PR title

[rany2]

I've noticed that FEDC sometimes creates PRs that downgrade the package (probably from a caching issue on the mirror's end). In this issue I'm proposing that the PR title/body be modified to specify the old version and the new version it's getting bumped to.

Example:

• Update chromium-101.0.4951.54.tar.xz from 101.0.4951.54 to 101.0.4951.64

[rany2]

This issue happens mostly in the Brave flatpak though, I think it might be better to add a check to make sure that the PR is upgrading and not downgrading instead.

[gasinvein]

The problem is, f-e-d-c doesn't know what the current version is - there is no such information stored in the manifest currently.
Kinda duplicate of #286, I'll rename and pin that one as a more generic issue.