feat(policy): adds new public keys table (#1836)

Implements the following ADR as discussed here
#1485.

- Adds new `public_keys` table along with mappings pivot tables for
attribute values, definitions and namespaces.
- On create key if there is a previous key with the same alg it will
make previous key inactive while mapping the the new key to the same
namespaces, attribute definitions and values.
  - On first mapping public key field `was_mapped` gets set to `true`
- Adds new CRUD RPC's to manage public keys and their associations
- Updates only allow metadata to be updated considering public keys
immutable
- Returns public keys on `GetAttributeValueByFQN` rpc
- Adds new ENUM values
  - `KAS_PUBLIC_KEY_ALG_ENUM_RSA_4096`
  - `KAS_PUBLIC_KEY_ALG_ENUM_EC_SECP384R1`
  - `KAS_PUBLIC_KEY_ALG_ENUM_EC_SECP521R1`

Author: strantalis