librarian: release soak time for Go SDK

> Got it, so the logic is set release level to `ga` if the version is equal to or larger than `1.0.0` and api path doesn't contain `alpha` and `beta`. Do you think this works?

I'm not sure...the first version of a new client is currently 0.1.0 set to, which, with this logic, would result in the releaseLevel being `beta` (even for `vN` api packages), only switching to `ga` when a `1.0.0` is forced e.g. via `--version`. Typing that out, it probably makes sense as an algorithm to start with.

I'd like to summon @jskeet for latest on "soak time" discussions though.

@JoeWang1127 keep in mind, idk how python or other languages use this

_Originally posted by @noahdietz in https://github.com/googleapis/librarian/issues/3961#issuecomment-3874795657_