Restructure headscale documentation (#2163)

* Setup mkdocs-redirects

* Restructure existing documentation

* Move client OS support into the documentation

* Move existing Client OS support table into its own documentation page
* Link from README.md to the rendered documentation
* Document minimum Tailscale client version

* Reuse CONTRIBUTING.md" in the documentation

* Include "CONTRIBUTING.md" from the repository root
* Update FAQ and index page and link to the contributing docs

* Add configuration reference

* Add a getting started page and explain the first steps with headscale

* Use the existing "Using headscale" sections and combine them into a
  single getting started guide with a little bit more explanation.
* Explain how to get help from the command line client.
* Remove duplicated sections from existing installation guides

* Document requirements and assumptions

* Document packages provided by the community

* Move deb install guide to official releases

* Move manual install guide to official releases

* Move container documentation to setup section

* Move sealos documentation to cloud install page

* Move OpenBSD docs to build from source

* Simplify DNS documentation

* Add sponsor page

* Add releases page

* Add features page

* Add help page

* Add upgrading page

* Adjust mkdocs nav

* Update wording

Use the term headscale for the project, Headscale on the beginning of a
sentence and `headscale` when refering to the CLI.

* Welcome to headscale

* Link to existing documentation in the FAQ

* Remove the goal header and use the text as opener

* Indent code block in OIDC

* Make a few pages linter compatible

Also update ignored files for prettier

* Recommend HTTPS on port 443

Fixes: #2164

* Use hosts in acl documentation

thx @efficacy38 for noticing this

Ref: #1863

* Use mkdocs-macros to set headscale version once

config-example.yaml

@@ -209,7 +209,7 @@ tls_letsencrypt_cache_dir: /var/lib/headscale/cache
 
 # Type of ACME challenge to use, currently supported types:
 # HTTP-01 or TLS-ALPN-01
-# See [docs/tls.md](docs/tls.md) for more information
+# See: docs/ref/tls.md for more information
 tls_letsencrypt_challenge_type: HTTP-01
 # When HTTP-01 challenge is chosen, letsencrypt must set up a
 # verification endpoint, and it will be listening on:
@@ -297,7 +297,7 @@ dns:
 
   # Extra DNS records
   # so far only A-records are supported (on the tailscale side)
-  # See https://github.com/juanfont/headscale/blob/main/docs/dns-records.md#Limitations
+  # See: docs/ref/dns.md
   extra_records: []
   #   - name: "grafana.myvpn.example.com"
   #     type: "A"