Feature request: Allow specifying the `buck2` path in `gobuckify`.

[kminehart]

We use a tool to help us manage our source code dependencies and if buck2 isn't in the $PATH then gobuckify fails:

2026/02/17 09:15:30 ERROR Error querying golist err="error querying golist for {darwin arm64 config//os:macos config//cpu:arm64}: failed to start go list: exec: \"buck2\": executable file not found in $PATH"
2026/02/17 09:15:30 ERROR Error querying golist err="error querying golist for {linux arm64 config//os:linux config//cpu:arm64}: failed to start go list: exec: \"buck2\": executable file not found in $PATH"
2026/02/17 09:15:30 ERROR Error querying golist err="error querying golist for {linux amd64 config//os:linux config//cpu:x86_64}: failed to start go list: exec: \"buck2\": executable file not found in $PATH"
2026/02/17 09:15:30 ERROR Error querying golist err="error querying golist for {darwin amd64 config//os:macos config//cpu:x86_64}: failed to start go list: exec: \"buck2\": executable file not found in $PATH"

Ideally we could run BUCK2=$(buck2) $(buck2) run prelude//go/tools/gobuckify:gobuckify -- .

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I have this working locally and plan on opening a PR soon, along with most of the other issues I will be opening :)