[bug]: MintAsset returns the entire MintingBatch, not just the currently minted PendingAsset

[ZZiigguurraatt]

The response of MintAsset (https://lightning.engineering/api-docs/api/taproot-assets/mint/mint-asset/index.html) is a MintAssetResponse object that contains one field, pending_batch which contains the entire MintingBatch and not just the currently minted PendingAsset. Therefor, we have no idea what asset we just minted if there are more than one PendingAsset and the pending assets have the same name. Also, we get in the response all pending assets from the batch this newly minted asset is a part of, which is a bit confusing and does not seem like it is data we should expect when minting an asset (I'm not sure why other assets in the batch are relevant to be included in the response when we never asked for them).

I think MintAsset should only return a PendingAsset object for the currently minted asset. Also, I think the PendingAsset object should include a batch_key so that we can then find the MintingBatch this asset is part of using the ListBatches RPC (https://lightning.engineering/api-docs/api/taproot-assets/mint/list-batches/index.html), if we want to. Using ListBatches is a more intentional way to request information on pending batches than just automatically sending as part of a response to MintAsset.