Btrfs progs release 6.3

[David Sterba <dsterba@suse.com>]

Hi,

btrfs-progs version 6.3 have been released.

There are some fixes and tweaks, the experimental status of block-group-tree
has been removed, namely the conversion but please still use it with care.

Otherwise there's nothing interesting from users' POV, more documentation is
being moved from archived wiki, updated tests.

The CI on github has been extended to cover devel and pre-release branches,
further enhancements are planned to do e.g. quick build tests for pull requests
or use self-hosted runners for heavier tests that may need to run against a
recent kernel. (https://github.com/kdave/btrfs-progs/actions)

Release process now uses more of the github features, so besides the tag itself
there's also a release with changelog (https://github.com/kdave/btrfs-progs/releases).
This allows to add "artifacts" i.e. other files besides the sources.

There are now static binaries published along with the release. They're built
inside the CI workflow "Static binaries" (also available there for download).
The upload is still done from an intermediate host so if you don't trust github
CI or me copying the files as-is, please build and use your own.

Please let me know if you have suggestions for improvements or if you find
problems with the CI/release things. It's new to me and I'm sure the are
already best practices to follow.

Changelog:
   * mkfs: option -R deprecated, options unified in -O (-R still works)
   * mkfs: fix potential race with udev leading to EBUSY due to repeatedly
     opened file descriptors
   * block-group-tree is out of experimental mode
      * available as 'mkfs.btrfs -O block-group-tree'
      * btrfstune can do in-place conversion to/from (use with care)
   * balance: fix recognizing old and new syntax
   * subvol snapshot: specific error if a failure is caused by an active swapfile
   * tree-stats: rephrase warning when run on a mounted filesystem
   * completion: 'filesystem du' also completes files
   * check: fix docs, help text and warning that --force + --repair works on a
     mounted filesystem
   * build: fix static build when static libudev is available
   * documentation:
      * more updates from wiki, developer docs, changelogs
      * reformatting
      * updates and fixes
   * other:
      * test updates and fixes
      * CI cleanups and old files removed
      * integration with Github actions

Tarballs: https://www.kernel.org/pub/linux/kernel/people/kdave/btrfs-progs/
Git: git://git.kernel.org/pub/scm/linux/kernel/git/kdave/btrfs-progs.git