Set up new website structure with MkDocs (#433)

Adapt current doc, Introduce MkDocs and plugins

• Adapt previous documentation structure to Mkdocs
• Introduce, configure, tweak Mkdocs and plugins/theme:
  • Material theme/framework, Mike (versions), coverage iframe integration, GitLab links

Set-up deployment workflow

• On main branch, in website job, build docs for a specific version, commit on pages branch, push commit on the remote from the job with access token
  • The coverage report is integrated in the website build. The artefact is retrieved from coverage job with needs: keyword
• From pages branch, an other pipeline is triggered, publishing the documentation website for all versions via GitLab Pages

Documentation content improvements

• Partially rework, and proofread current documentation
• Document documentation contribution

Close #433 (closed), #166 (closed)

doc/deathreaper.md

-# DeathReaper
-
-DeathReaper is a service reporting WoT exclusions on Discourse forums.
-Images are created containing Silkaj + DeathReaper.
-These images are operated on https://git.duniter.org/clients/python/deathreaper repository with schedule pipeline.
-
-### Installation
-
-When installing Silkaj, you have to specify `pydiscourse` extra in order to get DeathReaper dependency `pydiscourse` which will "activate" the command/feature.
-
-```sh
-pipx install silkaj[deathreaper]
-```
-
-If you are running the development environment with Poetry:
-
-```sh
-poetry install --extras deathreaper
-```
-
-### Usage
-
-DeathReaper was first available in a release from v0.12.0.
-Make sure `exclusions` command is present under `silkaj wot`, otherwise the installation when wrong.
-Then run `silkaj wot exclusions --help` to know how to use it.
-
-By default it will report the exclusions for last day from now till 24 hours in the past.
-You can specify an other duration `silkaj wot exclusions 0.5` for 12 hours.
-
-By default the report will be displayed in the terminal.
-To have it published on a Discourse forum, `--api-id` `--*-api-key`, `--publish` has to be passed.
-Further code changes have to be done in order to support additional Discourse forums.