starship: add presets option

[bandithedoge]

Description

Fixes #7297. Mirrors NixOS/nixpkgs@68543ba.

I'm not sure how to do test cases that don't have to be manually updated along with Starship. Is it alright to use IFD in the test and compare attrsets parsed from TOML?

Checklist

• Change is backwards compatible.

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[teto]

it's not a crucial setting so it's fine if not tested. IFD in tests would be fine I beleive. If someone can confirm it works, we can merge as is