allow --login to be used with nu's --commands parameter

[fdncred]

Description

This PR allows the --login/-l parameter to be used with nushell's --commands/-c parameter. When you do this, since you're invoking it with the -l flag, nushell will load your env.nu, config.nu, and login.nu, in that order. Then it will proceed to run your commands. I think this provides a better quality of life when you want to run scripts with your personal config files as a login shell.

Before (these entries are from the default_env.nu)

After (these entries are from my personal env.nu)

closes #9833

User-Facing Changes

Tests + Formatting

After Submitting

[amtoine]

changes look simple enough 👌

@balupton, i see you've added a 👍 to the PR, does that mean your issue is gone with it? 😇

[balupton]

@amtoine

So this works for nu -l -c {0]} to make it consistent with nu -l -e {0}, however there is no change to nu -l {0} despite nu -l loading the config files:

> cargo run  -- -l
    Finished dev [unoptimized + debuginfo] target(s) in 0.17s
     Running `/Users/balupton/.cargo/target/debug/nu -l`
Env
Config
Login
     __  ,
 .--()°'.' Welcome to Nushell,
'|, . ,'   based on the nu language,
 !_-(_\    where all data is structured!

Please join our Discord community at https://discord.gg/NtAbbGn
Our GitHub repository is at https://github.com/nushell/nushell
Our Documentation is located at https://nushell.sh
Tweet us at @nu_shell
Learn how to remove this at: https://nushell.sh/book/configuration.html#remove-welcome-message

It's been this long since Nushell's first commit:
4yrs 3months 26days 18hrs 3mins 45secs 623ms 940µs 

Startup Time: 169ms 569µs 250ns

~/Projects/nushell> exit                                  09/07/2023 07:03:00 PM
19:03:00:/Users/balupton/Projects/nushell:main
> cargo run  -- -l ~/Downloads/test.nu 
    Finished dev [unoptimized + debuginfo] target(s) in 0.17s
     Running `/Users/balupton/.cargo/target/debug/nu -l /Users/balupton/Downloads/test.nu`
File
19:03:13:/Users/balupton/Projects/nushell:main
> cargo run  -- -l -c ~/Downloads/test.nu
    Finished dev [unoptimized + debuginfo] target(s) in 0.17s
     Running `/Users/balupton/.cargo/target/debug/nu -l -c /Users/balupton/Downloads/test.nu`
Env
Config
Login
File

This is still a deviation from fish/zsh/bash, so not sure if Nushell team want to go further on this.

I'm happy as this this means I can adjust the CI testing for dorothy to just use nu -l -c instead of the current workaround that I am using:
https://github.com/bevry/dorothy/blob/b483848ed98201050d41b13529f0918da7a7c43d/.github/workflows/dorothy-workflow.yml#L53-L57

[fdncred]

I didn't look at nu -l <run_a_script> functionality yesterday with this PR. If someone else wants to do that, have at it.