The `push_registration_encryption_keys` map stores the
assymetric key pair generated on bouncer.
The public key will be used by the client to encrypt
registration data and the bouncer will use the corresponding
private key to decrypt.
- Updated the `generate_secrets.py` script to generate the map
during installation in dev environment.
- Added a management command to add / remove key i.e. use it
for key rotation while retaining the older key-pair for a period
of time.
