Complete registry pallet

[FaisalAl-Tameemi]

Data feeds must be registered into the oracle parachain and this can be done via a registry pallet.

The pallet's main responsibility is to be aware of data feeds (phat contracts) and keep track of them to use later. The pallet should also emit events when changes take place to a specific feed (added, removed, etc..).

Work done on the pallet can be found here.

The main 2 goals of this pallet would be as follows:

1. Register a feed
2. Unregister a feed

It should ideally also include some level of "approval" when registering and unregistering (this will be done via a democratic process later on -- i.e. a custom origin).

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This pallet should ideally contain 8 callable methods (extrinsics)

1. register_feed(): adds a new feed (API URL) to storage
2. unregister_feed(): removes an already registered feed from storage
3. xcm_register_feed(): handles an XCM message for a (consumer) parachain to subscribe
4. xcm_unregister_feed(): handles an XCM message for a (consumer) parachain to subscribe
5. register_consumer(): adds a consumer (AccountId) to storage
6. unregister_consumer(): removes an already registered consumer from storage
7. xcm_consumer_subscribe(): handles an XCM message for a (consumer) parachain to subscribe
8. xcm_consumer_unsubscribe(): handles an XCM message for a (consumer) parachain to subscribe

[FaisalAl-Tameemi]

• Make the response data type generic (i.e. [u8; 32])
• Name events and other variables generically