1013/expirable soulbound tokens support

[HaidarJbeily7]

Changes

• [x] Add SBT tokens support to Regulated assets pallet

  • Added more fieldsSoulboundTokenMetdata concerning Data Model in tech requirement.
  • Added update_sbt_expiration extrinsic. (This requirement is mentioned HERE)
  • Modified issue_sbt extrinsic with the new fields, added validation to allowed_assets and expires_at, and reverted the ISSUE_SBT permission checking.
  • Added check in regulate_asset extrinsic to not allow to regulate SBT.

• [x] Deny transfers for SBT tokens

  • Added this logic in AssetRegulator.check_permission(..)

• [x] Add expiration to SBT tokens

  • The expires_at field is optional, which achieves the optionality of expirable support.
  • Added expiration checking logic in AssetRegulator.check_permission(..)

• Thorough unit tests have been added to validate the new functionalities. These tests cover a wide range of scenarios to ensure robustness and correctness.

[HaidarJbeily7]

@vovac12 I modified the storage layout with your suggestions and modified the logic respectively.