SQL driver for OCM invitation manager

[gmgigi96]

This PR adds the sql driver for the OCM invitation manager, meant to be used in production.

Script to create sql tables:

CREATE TABLE ocm_tokens (
    token VARCHAR(255) NOT NULL PRIMARY KEY,
    initiator VARCHAR(255) NOT NULL,
    expiration DATETIME NOT NULL,
    description VARCHAR(255) DEFAULT NULL
);

CREATE TABLE ocm_remote_users (
    initiator VARCHAR(255) NOT NULL,
    opaque_user_id VARCHAR(255) NOT NULL,
    idp VARCHAR(255) NOT NULL,
    email VARCHAR(255) NOT NULL,
    display_name VARCHAR(255) NOT NULL,
    PRIMARY KEY (initiator, opaque_user_id, idp)
);