feat: reduce manual intervention required to initialize `midenup`'s `miden` command

Currently, in order to access the `miden` command manual intervention is required to add the `miden` symlink to the user's `$PATH`.
This can be a bit of a pain point in situations where a more automated approach is desired, like in a GitHub Action, like here for example: https://github.com/0xMiden/compiler/pull/896/changes#r2886279430.

A potential solution would be to have `midenup init` save the `miden` symlink directly in the default `~/.cargo/bin` directory

Look at the `midenup init` command's code to understand how it currently sets up the symlink. The goal is to modify it to place the symlink in `~/.cargo/bin` automatically. Check how the tool determines the user's PATH and handles permissions. Test the change by running the init command and verifying the symlink is created correctly without manual steps.

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