Support reusing PRs

[vaind]

Each time there's a new dependency version, a new PR is opened. This is because the branch name contains the target version. This approach was chosen so that users don't lose old PRs when a new, potentially incompatible, version comes out. On the other hand, when users don't want to update a dependency just yet, the new PRs start to pile up and the user has to manually close the old ones.

Originally raised on Discord: https://discord.com/channels/621778831602221064/750735628932612096/999556557752782920

Is there a way to instead of opening up new bump PRs, actually either close the old ones or just update them? e.g. getsentry/sentry-react-native#2378 and getsentry/sentry-react-native#2385
in case there are deps that we don't want to upgrade right away for some reason (eg compatibility), bump PRs are piling up.

Possible solutions:

1. switch the strategy, omitting the version name from the branch name. This, however, would duplicate all existing PRs too, so probably not something we would want to do without raising the version to v2
2. provide option to switch the strategy as described in the previous point, the default can stay as is,
3. start automatically closing old PRs with a matching branch name - here, the question is what to do with the branches... we s should probably delete them but not if there are some custom comits (made by a person, rather than the updater bot).

Currently, option nr. two sounds like both the simplest and most useful approach. Alternatively, we can go with option one (or two with a different default), while checking all repos using the updater (there are just a few now) and closing the duplicate PRs manually, if any.