Add a new option to trim the prompt

[kkpattern]

Feature Request

Is your feature request related to a problem? Please describe.

Thanks for this awesome tool. Currently, I have the following config:

format = """
$cmd_duration\
$line_break\
$hostname\
...
"""

I put cmd_duration on a separate line so that it can be more intuitively seen that it's the cost of the previous command:

starship on  trim_prompt
❯ nvim C:\Users\kyler\.config\starship.toml

took 58s
starship on  trim_prompt
❯

But it will leave an extra empty line if cmd_duration is not shown.

Describe the solution you'd like

We can add a new option, trim_prompt. When it's true, starship will trim the prompt, so there will be no extra empty line in the above case. The default value can be set to false for back compatibility.

I have a proof-of-concept implementation here: kkpattern@5800c6b. If this is OK, I'd happy to refine the code and prepare a PR.

Thanks.