public_key: Add support for "Simple Certificate Enrollment Protocol" to PKCS-7
Allow public_key:pem_entry_decode/2) to handle AES-128-CBC ciphered keys

Private keys generated by modern versions of ssh-keygen are ciphered
with AES-128-CBC instead of DES-EDE3-CBC.


Since DES-EDE3-CBC ciphered keys are handled, and the underlying
support for AES-128-CBC is already present, it seems a bug of omission
that AES-128-CBC ciphered keys are not.
Merge branch 'dotsimon/pubkey_aes_cbc/OTP-11281' into maint

* dotsimon/pubkey_aes_cbc/OTP-11281:
  Allow public_key:pem_entry_decode/2) to handle AES-128-CBC ciphered keys