docs: replace static documentation with client-side redirects (#404)

This commit replaces the legacy HTML documentation files with client-side
HTTP redirects (meta-refresh) to point users to the new documentation
site at https://cloudnative-pg.io/docs/.

Changes include:
- Replaced all `index.html` files in versions 1.27, 1.28, and 'current'
  with redirect stubs.
- Implemented specific version mapping logic:
    - 'current' now redirects to the 'devel' documentation.
    - Release candidates (e.g., 1.27.0-rc1) redirect to the
      major.minor version (1.27).
- Purged unnecessary assets (PNG, JPG, CSS, YAML, and 404.html) from
  the affected version directories to reduce repository bloat, as
  these folders now only serve as redirect bridges.

Work performed via automated script in `hack/create_http_redirects.sh`.

Signed-off-by: Jonathan Gonzalez V. <jonathan.abdiel@gmail.com>
Signed-off-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>
Co-authored-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>
Signed-off-by: Gabriele Bartolini <gabriele.bartolini@enterprisedb.com>

Author: sxd