Support upgradeable-program in 'anchor test'

[nickguo]

Hello, I have a self-motivated feature request to add support for --upgradeable-program to anchor test.

In my project, I'd like to test that certain instructions can only be executed by the program's upgrade authority. However, after poking around anchor test, I see that we always deploy the program with --bpf-program, so the upgrade authority is not available. https://github.com/coral-xyz/anchor/blob/master/cli/src/lib.rs#L3039

This led me to create a separate test script in order to unblock myself. In the long term, I would love to delete my test script and use built-in anchor test features instead.

Proposal

Add a boolean flag to anchor test to toggle deploying target program as upgradeable. Something like anchor test --test_upgradeable_program. The default behavior is still to use --bpf-program, unchanged from today.

If no objections, I'm happy to quickly proceed with a PR

[nickguo]

Change drafted here #2642