feat: migrate crab issuing to use pallet!

[songtianyi]

Part of #561.

Converts the crab backing pallet to the new pallet attribute macro introduced in #6877.

Upgrade guidelines used.

⚠️ Breaking Change ⚠️
From checking upgrade guidelines

storages now use PalletInfo for module_prefix instead of the one given to decl_storage: use of this pallet in construct_runtime! needs careful updating of the name in order to not break storage or to upgrade storage (moreover for instantiable pallet). If pallet is published, make sure to warn about this breaking change.

Common notes

• their Trait is renamed Config
• all storages are now generic over T
• module prefix used by storages is now the PalletInfo::name given by construct_runtime.
• no longer RawEvent.

The metadata for CrabIssuing before migration

  {
          name: CrabIssuing,
          storage: {
            prefix: DarwiniaCrabIssuing,
            items: [
              {
                name: TotalMappedRing,
                modifier: Default,
                type: {
                  Plain: MappedRing
                },
                fallback: 0x00000000000000000000000000000000,
                documentation: []
              }
            ]
          },
          calls: [],
          events: [
            {
              name: DummyEvent,
              args: [
                AccountId,
                RingBalance,
                MappedRing
              ],
              documentation: [
                 Dummy Event. [who, swapped *CRING*, burned Mapped *RING*]
              ]
            }
          ],
          constants: [
            {
              name: ModuleId,
              type: ModuleId,
              value: da/crais,
              documentation: []
            }
          ],
          errors: [],
          index: 33
        },

The metadata for CrabIssuing after migration

 {
          name: DarwiniaCrabIssuing,
          storage: {
            prefix: DarwiniaCrabIssuing,
            items: [
              {
                name: TotalMappedRing,
                modifier: Optional,
                type: {
                  Plain: MappedRing
                },
                fallback: 0x00,
                documentation: []
              }
            ]
          },
          calls: [],
          events: [
            {
              name: DummyEvent,
              args: [
                AccountId,
                RingBalance,
                MappedRing
              ],
              documentation: [
                 Dummy Event. [who, swapped *CRING*, burned Mapped *RING*]
              ]
            }
          ],
          constants: [
            {
              name: ModuleId,
              type: ModuleId,
              value: da/crais,
              documentation: []
            }
          ],
          errors: [],
          index: 33
        },