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- [x] Add new / update outdated documentation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: gsw
  version: 3.4.0

source:
  url: https://files.pythonhosted.org/packages/60/16/07a701ba09158d4b518061cc43ce689a0276156f9df28ff038e3550bec79/gsw-3.4.0.tar.gz
  sha256: d45c835af0e539235e9cf46ae58d9447e206d145b13ecfe7447ad7b8fbdcf86d

requirements:
  run:
    - numpy

test:
  imports:
    - gsw

about:
  home: https://github.com/TEOS-10/GSW-python
  PyPI: https://pypi.org/project/gsw
  summary: Gibbs Seawater Oceanographic Package of TEOS-10
  license: BSD

package:
  name: gsw
  version: 3.4.0

source:
  url: https://files.pythonhosted.org/packages/60/16/07a701ba09158d4b518061cc43ce689a0276156f9df28ff038e3550bec79/gsw-3.4.0.tar.gz
  sha256: d45c835af0e539235e9cf46ae58d9447e206d145b13ecfe7447ad7b8fbdcf86d

requirements:
  run:
    - numpy

test:
  imports:
    - gsw

about:
  home: https://github.com/TEOS-10/GSW-python
  PyPI: https://pypi.org/project/gsw
  summary: Gibbs Seawater Oceanographic Package of TEOS-10
  license: BSD
