[GEAR-6020] encrypt/decrypt

GEAR-6020 and GEAR-6021.

Adds encrypt/decrypt action, with special handling for DICOM files (non-DICOM encrypts in place; DICOM stores encrypted values in EncryptedAttributesSequence)

Adds dicom-only config option to retain the original value of all de-identified tags in EncryptedAttributesSequence

Allows for both symmetric (all file types) and asymmetric (dicom-only) encryption

Allows for symmetric encryption secret-key to be set at both global and FileProfile level

Allows for a list of public-key values to encrypt for multiple recipients

Docs updated to explain encrypt/decrypt