[FEATURE] Add support for EROFS

[darkspadez]

Add support for EROFS

Now that alpha support EROFS, add support in sysext-bakery to build sysexts in EROFS.

How to use

Specify $fmt as erofs

Testing done

Initial building on test machine seems to work and load but needs more testing to make sure no issues w/ Flatcar and EROFS sysexts.

[tormath1]

Thanks, a small note regarding the erofs usage.

[darkspadez]

@tormath1 My apologies that was from testing, I have updated the code with the correct mkfs command

    ----- ===== ##### Creating extension image 'kubernetes.raw' and generating SHA256SUM ##### ===== -----
mkfs.erofs 1.5
Build completed.
    ----- ===== ##### 'kubernetes.raw' is now ready ##### ===== -----

[tormath1]

@tormath1 My apologies that was from testing, I have updated the code with the correct mkfs command

    ----- ===== ##### Creating extension image 'kubernetes.raw' and generating SHA256SUM ##### ===== -----
mkfs.erofs 1.5
Build completed.
    ----- ===== ##### 'kubernetes.raw' is now ready ##### ===== -----

No worries, that looks better on my side too.

    ----- ===== ##### Creating extension image 'kubernetes.raw' and generating SHA256SUM ##### ===== -----
mkfs.erofs 1.8.4
Build completed.
------
Filesystem UUID: d80f0184-745e-4065-be50-48a09f906115
Filesystem total blocks: 72651 (of 4096-byte blocks)
Filesystem total inodes: 47
Filesystem total metadata blocks: 17
Filesystem total deduplicated bytes (of source files): 0
    ----- ===== ##### 'kubernetes.raw' is now ready ##### ===== -----

Added a note regarding the documentation on the requirements and we should be good to go.

[darkspadez]

Updated the readme

[tormath1]

Thanks a lot for your contribution!