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- [x] Add new / update outdated documentation

package:
  name: bleach
  version: 5.0.0
requirements:
  run:
    - webencodings
    - packaging
    - six
source:
  sha256: 08a1fe86d253b5c88c92cc3d810fd8048a16d15762e1e5b74d502256e5926aa1
  url: https://files.pythonhosted.org/packages/35/8b/bad37525e7ef0669f013059affb3bbcd9311a24d63eda96723339ee0aab7/bleach-5.0.0-py3-none-any.whl
test:
  imports:
    - bleach

package:
  name: bleach
  version: 5.0.0
requirements:
  run:
    - webencodings
    - packaging
    - six
source:
  sha256: 08a1fe86d253b5c88c92cc3d810fd8048a16d15762e1e5b74d502256e5926aa1
  url: https://files.pythonhosted.org/packages/35/8b/bad37525e7ef0669f013059affb3bbcd9311a24d63eda96723339ee0aab7/bleach-5.0.0-py3-none-any.whl
test:
  imports:
    - bleach
