Simplify the version bump process. ### Description

Simplify the version bump process.

- Use substitution hook in docs to update CDN URL.
  - In `dev` or `prerelease` versions, it will point to `dev` url
  - In `stable` versions, it will point it `vX.Y.Z` url
- Introduce a version bump script `tools/bump_version.py`.


~- Use `bump2version` to bump Python versions (continuing from #2460)~
~- Use `npm version` to bump JS versions~
~- Update `run_docker` script to use latest deployed pre-built docker image when `--pre-built` option is specified.~

### Checklists

- [x] Add new / update outdated documentation

from pyodide_test_runner import run_in_pyodide


@run_in_pyodide(packages=["Jinja2"])
def test_jinja2(selenium):
    import jinja2

    template = jinja2.Template("Hello {{ name }}!")
    content = template.render(name="Zach")
    assert content == "Hello Zach!"

from pyodide_test_runner import run_in_pyodide


@run_in_pyodide(packages=["Jinja2"])
def test_jinja2(selenium):
    import jinja2

    template = jinja2.Template("Hello {{ name }}!")
    content = template.render(name="Zach")
    assert content == "Hello Zach!"
