Update development.md

What does this MR do?

While setting up my gitlab-pages environment I got confused with some information on doc/development.md. It was also confusing to have some duplicated information in https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/main/doc/howto/pages.md.

I propose to have all the information regarding gitlab-pages development in one place (a Single Source Of Truth - SSOT). For that, I:

1. Revamped the gitlab-pages/doc/development.md to have all the required information to start a gitlab-pages developing environment (this MR)
2. If this MR is approve, I'll open another MR in the GDK repository to point the GDK/doc/howto/pages.md to the gitlab-pages/doc/development.md.

Related to: #730 (closed)

TODO

• I added the Changelog trailer (e.g. Changelog: added) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines