rework docker tags (#1763)

* rework docker tags

This commit tries to align the new docker tags with the old schema

A prerelease will end up with the following tags:

- unstable
- v0.23.0-alpha3
- 0.23.0.alpha3
- sha-1234adsfg

A release will end up with:

- latest
- stable
- v0.23.0
- v0.23
- v0
- 0.23.0
- 0.23
- 0
- sha-1234adsfg

All of the builds will also have a `-debug` version.

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

* update changelog

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

---------

Signed-off-by: Kristoffer Dalby <kristoffer@tailscale.com>

CHANGELOG.md

@@ -31,6 +31,8 @@ after improving the test harness as part of adopting [#1460](https://github.com/
   - If no DERP is configured, the server will fail to start, this can be because it cannot load the DERPMap from file or url.
 - Embedded DERP server requires a private key [#1611](https://github.com/juanfont/headscale/pull/1611)
   - Add a filepath entry to [`derp.server.private_key_path`](https://github.com/juanfont/headscale/blob/b35993981297e18393706b2c963d6db882bba6aa/config-example.yaml#L95)
+- Docker images are now built with goreleaser (ko) [#1716](https://github.com/juanfont/headscale/pull/1716) [#1763](https://github.com/juanfont/headscale/pull/1763)
+  - Entrypoint of container image has changed from shell to headscale, require change from `headscale serve` to `serve`
 
 ### Changes