feat: Runner image variants, CI improvements (#306)

## Description

Next step would be having full DE environment variant I guess? I'll see
later if it's doable in this PR or if I'll do separate one for keeping
things small and manageable for once 😅

- Added easily doable variants for runners, with simple CI build matrix.
- Added playsite in CI builds finally.
- Some CI formatting and naming fixes.
- Removed PR full runner builds as they kept failing due to lack of disk
space on GH runner.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* New dedicated runner images for Steam, Heroic, and Minecraft plus a
common runtime and builder images.
* **Chores**
* CI/workflow reorganization to build and publish more runner variants
and base images.
* Installer and package tweaks (package manager flags, CUDA enablement)
and updated build tooling.
* Unified startup to use a constructed launch command; removed two
default environment exports.
  * Added container ignore patterns.

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settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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Co-authored-by: DatCaptainHorse <DatCaptainHorse@users.noreply.github.com>

.github/workflows/relay.yml

@@ -1,6 +1,5 @@
-#Tabs not spaces, you moron :)
+name: Build Nestri relay
 
-name: Build nestri:relay
 on:
     pull_request:
         paths: