Add try/catch functionality (#7221)

# Description

This adds `try` (with an optional `catch` piece). Much like other
languages, `try` will try to run a block. If the block fails to run
successfully, the optional `catch` block will run if it is available.

# User-Facing Changes

This adds the `try` command.

# 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

@@ -60,6 +60,7 @@ pub fn create_default_context() -> EngineState {
             Metadata,
             Module,
             Mut,
+            Try,
             Use,
             Version,
             While,