Add diff/log commands

[PierreLoupG]

Add two new commands, diff and log.

The diff command shows the current revision differences of all sources compared to the referenced revision in the menu.

$ cooker diff
poky: dunfell-23.0.0 .. dunfell-23.0.13
meta-openembedded: ab9fca4 .. 321dc39

The log command prints the changes (added, modified, deleted) of the build sources between two menu versions. The formatted output can be appended to a changelog file for release.

$ cooker log qemux86 menu.old.json -H meta-openembedded -o md
## Added projects
- meta-d at revision 895fac4

## Modified projects
- meta-openembedded changed from ab9fca4 to 321dc39
  - 321dc39b3 commit message
  - ef65938fd commit message
- meta-b changed from 5d2abf6 to 37f332a

## Deleted projects
- meta-common at revision 0c560e7

Test for the log command added in the test-suit.

[pboettch]

Looks good. Could you please run pylint on your changed and see whether all corrections make sense? I saw, e.g., 2 empty lines between classes and functions are not there.

[cpb-]

Thanks Pierre-Loup !