ci: AWS instance review and improved build caching

* Tone down the performance of some runners from 8cpu+ down to 4cpu+
* Improve and document caching on PX4 builds with an improved ccache key strategy
* Review and document artifact upload logic for binaries uploaded to S3 and github
releases
* Future Improvement, introduce runners configuration file so we can
control more precesily which instances are allocated.

Signed-off-by: Ramon Roche <mrpollo@gmail.com>

.github/workflows/flash_analysis.yml

@@ -24,7 +24,7 @@ env:
 jobs:
   analyze_flash:
     name: Analyzing ${{ matrix.target }}
-    runs-on: [runs-on,runner=8cpu-linux-x64,image=ubuntu24-full-x64,"run-id=${{ github.run_id }}",spot=false]
+    runs-on: [runs-on,runner=4cpu-linux-x64,image=ubuntu24-full-x64,"run-id=${{ github.run_id }}",spot=false]
     container:
       image: px4io/px4-dev:v1.16.0-rc1-258-g0369abd556
     strategy:
@@ -97,7 +97,7 @@ jobs:
   # Track this issue https://github.com/PX4/PX4-Autopilot/issues/24408
   post_pr_comment:
     name: Publish Results
-    runs-on: [runs-on,runner=1cpu-linux-x64,image=ubuntu24-full-x64,"run-id=${{ github.run_id }}",spot=false]
+    runs-on: [runs-on,runner=1cpu-linux-x64,image=ubuntu24-full-x64,"run-id=${{ github.run_id }}"]
     needs: [analyze_flash]
     env:
       V5X-SUMMARY-MAP-ABS: ${{ fromJSON(fromJSON(needs.analyze_flash.outputs.px4_fmu-v5x-bloaty-summary-map).vm-absolute) }}