feat(docs): add setAllowedExecutor function details for minting tags

Author: fassko

docs/fassets/reference/IMintingTagManager.mdx

@@ -120,3 +120,20 @@ function allowedExecutor(uint256 _mintingTag) external view returns (address);
 #### Returns
 
 - The address of the allowed executor, or `address(0)` if none is set.
+
+### `setAllowedExecutor`
+
+Set the allowed executor for a tag.
+Only callable by the tag owner.
+The allowed executor is the only address that can execute direct mintings with this tag.
+Setting an allowed executor is optional; if not set, anyone can execute mintings with the tag.
+Changes to the allowed executor are subject to a cooldown delay before they become active.
+
+```solidity
+function setAllowedExecutor(uint256 _mintingTag, address _executor) external;
+```
+
+#### Parameters
+
+- `_mintingTag`: The minting tag ID.
+- `_executor`: The new allowed executor address (must not be the zero address).