Allow user to override version of sandbox binary

[austinabell]

Currently, the master branch with a specific commit is used for the bin_url, but it would be beneficial if a user could override this with their own URL or just be able to customize the commit/version to be able to test against older/newer versions.

Ideally using this env variable (or helper function) would overwrite the existing binary if one already exists instead of skipping checks if the binary is already installed.

[mohamedalichelbi]

By removing the commit hash from this line I got the latest binary (1.25.0) even though mainnet is on 1.24.0
I think ideally integration tests should run whatever is live on mainnet per default, but I agree that ability to control this would be very helpful