PBS-39 feature: Add binlog encryption config and keyring support (part 3)

[percona-ysorokin]

https://perconadev.atlassian.net/browse/PBS-39

'binsrv::binlog_file_metadata' class extended with additional optional field 'encryption' of class 'binsrv::binlog_file_encryption_metadata' that consists of two fields:

• 'file_key_envelope' holding info about file key encryption,
• 'file_data_envelope' holding info about binlog data file encryption.

Added new 'binsrv::file_key_envelope' class with the following fields:

• 'kek_id' - the identifier of the key from the keyring that was used as KEK for file key encryption operation,
• 'iv_hex' - the initialization vector that was used for this file key encryption operation (optional, should be set for every mode apart from 'XXX-ECB'),
• 'data_hex' - the result of the key-encryption operation,
• 'tag_hex' - the AEAD tag calculated as the result of this file key encryption operation (optional, is set only in 'XXX_GCM' encryption modes).

Added new 'binsrv::file_data_envelope' class with the following fields:

• 'cipher' - the name of the encryption cipher used for binlog file data encryption operation (e.g. 'AES-256-CTR'),
• 'iv_hex' - the initialization vector that was used for this binlog file data encryption operation (always present as file data encryption operation requires a streaming cipher like 'XXX-CTR' or 'XXX-GCM'),
• 'tag_hex' - the AEAD tag calculated as the result of this binlog file data encryption operation (optional, is set only in 'XXX-GCM' encryption modes).

'binsrv::basic_keyring' interface extended with one more method 'contains()' which checks if a key with the specified identifier present in the keyring.

'binsrv::storage::binlog_record' internal class extended with additional optional 'encryption' field of class 'binsrv::storage::binlog_encryption_record' which holds info from the envelopes above in the form more suitable for encryption / decryption operations (unhexed).

If encryption is enabled in the main configuration file each JSON binlog metadata file will now include additional 'encryption' subelement. 'save_binlog_metadata()' / 'load_binlog_metadata()' methods in the 'binsrv::storage' class extended with converting encryption envelopes from / to internal 'binsrv::storage::binlog_encryption_record' class instances.

As an intermediate step added fake file key / iv generation functions, file key encryption and file key encryption tag calculation functions, fake file data encryption and file data encryption tag calculation functionality to the 'binsrv::storage::generate_binlog_encryption_record()' method. At the next step these functions should be replaced with proper OpenSSL calls.