Bugfix: AttributeError exceptions when using codemagic.models.certificate

[priitlatt]

The internals of codemagic.models.Certificate rely heavily on X.509 certificate implementation OpenSSL.crypto.X509 from pyOpenSSL module.

Lately there have been number of conflicts (and consequently bugs in this repo) due to incompatibilities between pyOpenSSL and cryptography (such as #217). It is also strongly encouraged to replace pyOpenSSL usages with cryptography where possible (see the note on PyPI description).

Considering the above, codemagic.models.Certificate was refactored to use cryptography.x509.Certificate internally instead of OpenSSL.crypto.X509.

Changes were tested with the following pyOpenSSL and cryptography version combinations:

• pyOpenSSL version 19.0.0 and cryptography versions 3.3.1, 35.0.0, 36.0.2, 37.0.1 and 37.0.2.
• pyOpenSSL version 19.1.0 and cryptography versions 3.3.1, 35.0.0, 36.0.2, 37.0.1 and 37.0.2.
• pyOpenSSL version 20.0.0 and cryptography versions3.3.1, 35.0.0, 36.0.2, 37.0.1 and 37.0.2.
• pyOpenSSL version 20.0.1 and cryptography versions 3.3.1, 35.0.0, 36.0.2, 37.0.1 and 37.0.2.
• pyOpenSSL version 21.0.0 and cryptography versions 3.3.1, 35.0.0, 36.0.2, 37.0.1 and 37.0.2.
• pyOpenSSL version 22.0.0 and cryptography versions 3.3.1, 35.0.0, 36.0.2, 37.0.1 and 37.0.2.

Note that cryptography version 37.0.0 is still not supported and remains excluded from the allowed versions (also in setup.py).

[VeArnold]

Left one minor comment, up to you, other than that LGTM