chore: token policies persisted in DB

[Stellatsuu]

Closes: #524

Changes:

• Moved the dirac_policies from TokenPayload to RefreshTokensPayload and AccessTokenPayload.
  Later, this should be removed from RefreshTokensPayload.

• RefreshTokens now has a policies column.
  Manual updates to the already existing DBTable is needed: ALTER TABLE RefreshTokens ADD COLUMN Policies JSON. It should add NULL by default for existing values.

• Policies are added from all_access_policies in the exchange_token function if no policies were found in the DB (e.g, new RefreshToken). Otherwise, they are taken from the DB to create a new AccessTokenPayload.

• mint_token function doesn't need to enrich the token anymore since the payloads already have the policies inside them, from exchange_token function.

• enrich_token function now takes only the AccessTokenPayload and returns one dict with the policies values.