Use fish_add_path in foundryup installation

[bojidar-bg]

Component

Foundryup

Have you ensured that all of these are up to date?

• Foundry
• Foundryup

What version of Foundry are you on?

forge 0.2.0 (f5c9199 2023-12-01T00:19:29.279040779Z)

What command(s) is the bug in?

No response

Operating System

Linux

Describe the bug

The foundryup installation script (https://foundry.paradigm.xyz / foundryup/install) modifies config.fish directly, but fish shell provides a simpler / more idiomatic ^{e.g. see Arch wiki} way of modifying the path using fish_add_path. ence the following:

fish_add_path --append ~/.foundry/bin

will immediately add (realpath ~/.foundry/bin) at the end of PATH in all fish shells (deduplicated), and will persist it across reboots (due to how universal variables work in fish) -- there is no need to modify config.fish.