add a new inspect command for more debugging (#8028)

# Description

The purpose of this command is to help to debug pipelines. It works by
allowing you to inject the `inspect` command into a pipeline at any
point. Then it shows you what the input description is and what the
input values are that are passed into `inspect`. With each step it
prints this information out while also passing the value information on
to the next step in the pipeline.


![image](https://user-images.githubusercontent.com/343840/218154064-e107859b-d0da-41c6-8e34-2d717639b81c.png)

This command is kind of a "hack job" because it clones maybe too much
and I had to get creative in order to output two different tables. I'm
sure there are many ways this can be improved or combined into other
commands but I wanted to start here. Note that the `inspect` output is
written to stderr and the normal nushell output is written to stdout. If
we were to output both to stdout, nushell would get confused.

# User-Facing Changes



# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/default_context.rs

@@ -175,6 +175,7 @@ pub fn create_default_context() -> EngineState {
             Complete,
             Explain,
             External,
+            Inspect,
             NuCheck,
             Sys,
             TimeIt,