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- [x] Add new / update outdated documentation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: docutils
  version: 0.18.1
source:
  sha256: 23010f129180089fbcd3bc08cfefccb3b890b0050e1ca00c867036e9d161b98c
  url: https://files.pythonhosted.org/packages/8d/14/69b4bad34e3f250afe29a854da03acb6747711f3df06c359fa053fae4e76/docutils-0.18.1-py2.py3-none-any.whl
test:
  imports:
    - docutils

package:
  name: docutils
  version: 0.18.1
source:
  sha256: 23010f129180089fbcd3bc08cfefccb3b890b0050e1ca00c867036e9d161b98c
  url: https://files.pythonhosted.org/packages/8d/14/69b4bad34e3f250afe29a854da03acb6747711f3df06c359fa053fae4e76/docutils-0.18.1-py2.py3-none-any.whl
test:
  imports:
    - docutils
