feat: Add custom completer for cargo <TAB> to cargo scripts

[dhruv-38]

What does this PR try to resolve?

Tracking issue #14520
Add a custom completer for cargo <TAB> to cargo scripts

This PR introduces auto-completion for the cargo <TAB> option. When a user types cargo <TAB> and presses the TAB key, the system will also automatically suggest scripts defined in config.toml for the current working directory

How should we test and review this PR?

To verify this feature, follow these steps:
-In the terminal, type cargo <TAB>
-Press the TAB key.
-You should also see the scripts for the project.

[rustbot]

r? @epage

rustbot has assigned @epage.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: @ehuss, @epage, @weihanglo
• @ehuss, @epage, @weihanglo expanded to ehuss, epage, weihanglo
• Random selection from ehuss, epage, weihanglo

[epage]

This has nothing to do with Cargo Script completions.

On top of that, we shouldn't be offering Cargo Script completions until #16569 is merged.