feat: Add docs for two new execution errors related to canister_metadata

docs/references/execution-errors.mdx

@@ -740,6 +740,27 @@ An example of this error is:
 
 To fix this error, ensure that you are a controller of the canister that the snapshot belongs to.
 
+### Canister metadata no Wasm module
+
+This indicates that you are trying to fetch the metadata of a canister while there is no Wasm module installed on that canister.
+
+An example of this error is:
+```
+  The canister xxx-xxx has no Wasm module and hence no metadata is available.
+```
+
+To fix this error, install a Wasm module with the given metadata section if you are a controller of the canister.
+
+### Canister metadata section not found
+
+This indicates that you are trying to fetch a metadata section that either does not exist, or that is private while you are not a controller of the canister.
+
+An example of this error is:
+```
+  The canister xxx-xxx has no metadata section with the name yyy-yyy.
+```
+
+To fix this error, make sure the metadata section exists for the given canister and section name. In the case of a private section, make sure the message is signed by a principal that is a controller of the canister.
 
 [canbench]: /docs/building-apps/advanced/benchmarking