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 -->

---------

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

.github/workflows/docker-bake.hcl

@@ -3,14 +3,14 @@ variable "BASE_IMAGE" {
 }
 
 group "default" {
-  targets = ["runner"]
+  targets = ["runner-base", "runner-builder"]
 }
 
 target "runner-base" {
   dockerfile = "containerfiles/runner-base.Containerfile"
   context    = "."
   args = {
-    BASE_IMAGE = "${BASE_IMAGE}"
+    BASE_IMAGE = BASE_IMAGE
   }
   cache-from = ["type=gha,scope=runner-base-pr"]
   cache-to = ["type=gha,scope=runner-base-pr,mode=max"]
@@ -30,19 +30,3 @@ target "runner-builder" {
     runner-base = "target:runner-base"
   }
 }
-
-target "runner" {
-  dockerfile = "containerfiles/runner.Containerfile"
-  context    = "."
-  args = {
-    RUNNER_BASE_IMAGE    = "runner-base:latest"
-    RUNNER_BUILDER_IMAGE = "runner-builder:latest"
-  }
-  cache-from = ["type=gha,scope=runner-pr"]
-  cache-to = ["type=gha,scope=runner-pr,mode=max"]
-  tags = ["nestri-runner"]
-  contexts = {
-    runner-base    = "target:runner-base"
-    runner-builder = "target:runner-builder"
-  }
-}