add metadata access command (#13785)

# Description
Add `metadata access`, which allows accessing/inspecting the metadata of
a stream in a closure.
```nu
ls | metadata access {|meta|
    ...
}
```

- The metadata is provided as an argument to the closure, identical to
the record obtained with `metadata` command.

- `metadata access` passes its input stream into the closure as it is.

- Within the closure, both the metadata and the stream are available.
The closure may modify, collect or pass the stream as it is.

# Motivation
- Without this command, nu code can't act on metadata without losing the
stream, use cases requiring both the stream and metadata must be
implemented either as a built-in or a plugin.

- This command allows users to enhance presentation of data, similar to
`table` coloring the output of `ls`.

crates/nu-command/src/default_context.rs

@@ -151,6 +151,7 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Explain,
             Inspect,
             Metadata,
+            MetadataAccess,
             MetadataSet,
             TimeIt,
             View,