Update QuickStart contents

Going to make a checklist so we can collect many small feedbacks :)

[quickstart](https://geonetwork-opensource.org/manuals/trunk/eng/users/user-guide/quick-start/index.html):

* [ ] assumes installation and/or docker available
* "after going through installer steps" ... install instructions under "maintainer guide" is appropriate? No that page is empty...
* "when you use docker" - but no docker instructions are anywhere to be found

Indeed this quickstart page is the top pick when searching for docker instructions for geonetwork.

* [ ] Recommend: include install instructions here, no discussion of trade-offs like maintainer section, just step by step instructions installation
* [ ] installer quickstart page, step by step instructions from download to running `start.bat`
* [ ] tomcat quickstart page (replacing a war install instructions)
* [ ] docker quickstart page (recommend: Include docker instructions, or link to them)

Recommendation:

* [ ] Adopt a numbered step approach or template
* [ ] Break into individual pages?
* [ ] Adopt consistent RST syntax to avoid basic markup, and make use of directives (see Sphinx [RST Style guide](https://gdal.org/contributing/rst_style.html) )

See:

* [GeoNetwork Orientation](https://docs.google.com/presentation/d/13e2q9zbF6glZmlcdC_2CrSdAUPkLZTn-2RS64hmWL9c/edit?usp=sharing) which has point form notes of all the different installation options