Add AES-CBC

[l1h3r]

Description of change

Adds AES-CBC HMAC SHA2 algorithms defined in rfc7518 for JSON web tokens used in identity.rs

Type of change

• Enhancement (a non-breaking change which adds functionality)

How the change has been tested

RFC test vectors

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[nothingismagick]

You know, this sort of thing REALLY seems like it should be a procedure in stronghold tbh. But I understand why you need it here.

[felsweg-iota]

Looks good to me. Please let @Wollac approve as well.

[semenov-vladyslav]

Looks good enough. But there's a few minor things to improve upon.

[semenov-vladyslav]

Please use feature = "aes-gcm" in tests/aead.rs