make parse -r columns return 0-indexed uncapitalised (#7897)

# Description

Fixes #7886.

```
/home/gabriel/CodingProjects/nushell〉'A|B|C' | parse -r '(\w)\|(\w)\|(\w)'                                                                                             01/29/2023 01:08:29 PM
╭───┬──────────┬──────────┬──────────╮
│ # │ capture0 │ capture1 │ capture2 │
├───┼──────────┼──────────┼──────────┤
│ 0 │ A        │ B        │ C        │
╰───┴──────────┴──────────┴──────────╯
```

# User-Facing Changes
Columns automatically named by `parse -r` are now 0-indexec and
uncapitalised.

# 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/tests/commands/parse.rs

@@ -144,7 +144,7 @@ mod regex {
                     open nushell_git_log_oneline.txt
                     | parse --regex "(\\w+) (.+) \\(#(\\d+)\\)"
                     | get 1
-                    | get Capture1
+                    | get capture0
                 "#
             ));
 
@@ -163,7 +163,7 @@ mod regex {
                     open nushell_git_log_oneline.txt
                     | parse --regex "(?P<Hash>\\w+) (.+) \\(#(?P<PR>\\d+)\\)"
                     | get 1
-                    | get Capture2
+                    | get capture1
                 "#
             ));