Drop custom AES encryption contexts in favor of parameter store

[andrewkrug]

Consider cutting out the code that loads and decrypts the key in favor of using parameter store:

lime-compiler/lib/lime-compiler/gpg.rb

Line 28 in f2035fb

def import_key kms_opts

[joelferrier]

I'm not opposed to using parameter store where it makes sense but last time I checked parameter store has the same limitation as encrypting directly against a kms key and doesn't allow encrypted parameters larger than 4k.

If this has changed then we can store the gpg key directly in parameter store as an encrypted parameter.
If we can't use encrypted parameter store secrets I'm hesitant to stop using the data key generated from a kms key.

Either way the setup process could use some love, perhaps a sub-command or a better helper script to securely store a gpg key.