Add support for reading Fortinet firmware files

[yunzheng]

This adds transparant decompression and deobfuscation of Fortinet firmware files via the FortiFirmwareContainer and FortiFirmwareFile classes.

The filename has to end with -FORTINET.out for it to be detected as a Fortinet firmware file.

Example usage:

$ target-shell FGT_VM64-v7.4.3.F-build2573-FORTINET.out
$ target-fs FGT_2000E-v5-build1673-FORTINET.out ls /migadmin

Or to decompress and deobfuscate a firmware file to stdout:

$ python3 -m dissect.target.containers.fortifw <FIRMWARE FILE> | xxd

Closes #655

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 85.50725% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 74.83%. Comparing base (12a4e46) to head (cd0d196).
Report is 1 commits behind head on main.

❗ Current head cd0d196 differs from pull request most recent head 42f3971. Consider uploading reports for the commit 42f3971 to get more accurate results

Files	Patch %	Lines
dissect/target/containers/fortifw.py	85.40%	20 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #652      +/-   ##
==========================================
- Coverage   74.84%   74.83%   -0.01%     
==========================================
  Files         288      288              
  Lines       23932    24038     +106     
==========================================
+ Hits        17912    17990      +78     
- Misses       6020     6048      +28     

Flag	Coverage Δ
unittests	74.83% <85.50%> (-0.01%)	⬇️

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