docs: add documentation for TransferAuthorization (#3044)

* transferauthz docs

(cherry picked from commit 79b349a)

docs/.vuepress/config.js

@@ -325,6 +325,11 @@ module.exports = {
                   directory: false,
                   path: "/apps/transfer/params.html",
                 },
+                {
+                  title: "Authorizations",
+                  directory: false,
+                  path: "/apps/transfer/authorizations.html",
+                },
               ],
             },
           ],

docs/apps/transfer/authorizations.md

@@ -0,0 +1,47 @@
+# `TransferAuthorization`
+
+`TransferAuthorization` implements the `Authorization` interface for `ibc.applications.transfer.v1.MsgTransfer`. It allows a granter to grant a grantee the privilege to submit MsgTransfer on its behalf. Please see the [Cosmos SDK docs](https://docs.cosmos.network/v0.47/modules/authz) for more details on granting privileges via the `x/authz` module.
+
+More specifically, the granter allows the grantee to transfer funds that belong to the granter over a specified channel.
+
+For the specified channel, the granter must be able to specify a spend limit of a specific denomination they wish to allow the grantee to be able to transfer.
+
+The granter may be able to specify the list of addresses that they allow to receive funds. If empty, then all addresses are allowed.
+
+
+It takes: 
+
+- a `SourcePort` and a `SourceChannel` which together comprise the unique transfer channel identifier over which authorized funds can be transferred.
+
+- a `SpendLimit` that specifies the maximum amount of tokens the grantee can spend. The `SpendLimit` is updated as the tokens are spent. This `SpendLimit` may also be updated to increase or decrease the limit as the granter wishes.
+
+- an `AllowList` list that specifies the list of addresses that are allowed to receive funds. If this list is empty, then all addresses are allowed to receive funds from the `TransferAuthorization`.
+
+Setting a `TransferAuthorization` is expected to fail if:
+- the spend limit is nil
+- the denomination of the spend limit is an invalid coin type
+- the source port ID is invalid
+- the source channel ID is invalid
+- there are duplicate entries in the `AllowList`
+
+Below is the `TransferAuthorization` message:
+
+```golang
+func NewTransferAuthorization(allocations ...Allocation) *TransferAuthorization {
+	return &TransferAuthorization{
+		Allocations: allocations,
+	}
+}
+
+type Allocation struct {
+	// the port on which the packet will be sent
+	SourcePort string 
+	// the channel by which the packet will be sent
+	SourceChannel string 
+	// spend limitation on the channel
+	SpendLimit sdk.Coins  
+	// allow list of receivers, an empty allow list permits any receiver address
+	AllowList []string 
+}
+
+```