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- [x] Add new / update outdated documentation

[metadata]
name = pyodide-build
version = 0.20.0dev0
author = Pyodide developers
description = "Tools for building Pyodide"
long_description = file: README.md
long_description_content_type = text/markdown
url = https://github.com/pyodide/pyodide
project_urls =
    Bug Tracker = https://github.com/pyodide/pyodide/issues
    Documentation = https://pyodide.org/en/stable/
classifiers =
    Programming Language :: Python :: 3
    License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)
    Operating System :: OS Independent

[options]
package_dir =
    = .
packages = find:
python_requires = >=3.10
install_requires =
    pyyaml
    cython<3.0
    ruamel.yaml
    packaging
    wheel
    tomli
    build==0.7.0

[options.entry_points]
console_scripts =
    pyodide-build = pyodide_build.__main__:main

[options.extras_require]
test =
    pytest

[options.packages.find]
where = .

[metadata]
name = pyodide-build
version = 0.21.0.dev0
author = Pyodide developers
description = "Tools for building Pyodide"
long_description = file: README.md
long_description_content_type = text/markdown
url = https://github.com/pyodide/pyodide
project_urls =
    Bug Tracker = https://github.com/pyodide/pyodide/issues
    Documentation = https://pyodide.org/en/stable/
classifiers =
    Programming Language :: Python :: 3
    License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)
    Operating System :: OS Independent

[options]
package_dir =
    = .
packages = find:
python_requires = >=3.10
install_requires =
    pyyaml
    cython<3.0
    ruamel.yaml
    packaging
    wheel
    tomli
    build==0.7.0

[options.entry_points]
console_scripts =
    pyodide-build = pyodide_build.__main__:main

[options.extras_require]
test =
    pytest

[options.packages.find]
where = .
