Release 2.0

[aignas]

Just starting this because this will need discussion/notes and documentation on breaking changes that we will need to do.

Potentially incompatible changes:

• [ ] #3117 - flip script to bootstrap.
• [ ] #2156 - flip venv/site-packages to true.
• [ ] experimental_index_url is enabled by default to all.
• [ ] We only support bazel 8 and 9.
• [ ] We remove protobuf aliases and deps.
• [ ] We remove Python 2 support fully.

Other milestones that I would like to include hit:

• [ ] pip.default and pip.configure will be stable.
• [ ] py.lock files can be read.

I would say we probably should aim for a particular date and whatever is ready is ready at that time.