dim: add support for applying patches using b4

Add 'b4-shazam-branch' and 'b4-shazam' subcommands to apply a patch
series using b4 [1], fetching the patches from Lore. You can either
specify the series using message-id on the command-line, or by piping a
message in the series to the subcommand. Additional b4 command-line
options may be specified as needed, for example to apply individual
patches.

b4 is a much more robust alternative to pretty much everything we do in
dim_apply_branch() and apply_patch() functions, and automatically
gathers reviews and acks from the list.

Use the b4.trailers-ignore-from config to ignore trailers from CI and
kernel build bot. b4 v0.13 or later is required to filter all trailers
in messages from the mentioned addresses (for example Fixes:
trailers). Otherwise b4 shazam picks up a lot of garbage trailers from
CI mails.

[1] https://b4.docs.kernel.org/en/latest/index.html



v3:
- Unconditionally require b3 v0.13 or later
- Use --config option instead of env vars
- Add DIM_B4 config option

v2:
- Use GIT_CONFIG_* to set b4.linkmask (Lucas)
- Use GIT_CONFIG_* to set b4.trailers-ignore-from
- Check for b4 command
- Check b4 version for cover trailers
- Use subcommand names b4-shazam and b4-shazam-branch

Signed-off-by: Jani Nikula <jani.nikula@intel.com>