Seperating firmware-utils into seperate repo

[Joseph Mullally]

> Most in-house OpenWrt packages are actually stored in their
> own git repo, see https://git.openwrt.org/ down in the
> /project/something_something.git
>
>  -Alberto

Thanks for the good suggestions Alberto. I still think it will be a
messy process for most new device contributors (where a lot of these
PRs will come from) and reviewers alike, as Adrian points out in the
"post-merge" peer review discussion above.

Overall I can't see what the real benefits of this change are. Unless
it really is official OpenWRT policy to release these as generic
firmware tools for use by other projects, and it absolutely has to be
a separate git repo. On many levels that's a good idea but also
nebulous. E.g. for the xiaomifw vacuum example, why not put it in its
own seperate upstream repo.

Anyway, maybe people disagree and are OK with this.

At a minimum to finish out this package split, someone needs to do this?
* Create a GitHub mirror for https://git.openwrt.org/project/firmware-utils.git

To avoid chaos in the future (or even now with 22.03, bugfixes, backports etc):
* Release branches for "firmware-utils.git" matching "openwrt.git"
(unless some versioning strategy like SEMVER is planned, but the
OpenWRT release branches seem the simplest)

Thanks,
- Joe