[ot] Restructure the release tarball and update the ci

[pamaury]

This commit restructure the archive to look like this:

.
├── build
│   ├── qemu-img
│   └── qemu-system-riscv32
└── scripts
    └── opentitan
        ├── flashgen.py
        └── otpconv.py

It also permutes the src and build arguments for the release script because it makes more sense.

Context: the idea is to make it easier to develop on qemu while using bazel. The bazel is still WIP but the intention is that one will be able to use it either with an official release, or a a local checkout since they have the same directory structure.

[rivos-eblot]

I'm not using Bazel so I'm of a little help for this case. The script looks fine.

[pamaury]

@rivos-eblot can you approve/merge the PR?

[HU90m]

For context: https://github.com/lowRISC/opentitan/pull/19420#issuecomment-1689727584