Respect scaling_reserved_ram feature flag

The amount of RAM given to the CodeQL evaluator is the machine's total
memory size, minus a reserved amount. Currently, the reserved amount is
fixed at 1 GB (or 1.5 GB on Windows). When the scaling_reserved_ram
feature flag is enabled, we also add 2% of the total memory size to the
reserved amount. This allows for the fact that the kernel will consume
more RAM (e.g. for page tables) on machines with more physical RAM.

src/feature-flags.ts

@@ -39,6 +39,7 @@ export enum Feature {
   MlPoweredQueriesEnabled = "ml_powered_queries_enabled",
   NewAnalysisSummaryEnabled = "new_analysis_summary_enabled",
   QaTelemetryEnabled = "qa_telemetry_enabled",
+  ScalingReservedRam = "scaling_reserved_ram",
   UploadFailedSarifEnabled = "upload_failed_sarif_enabled",
 }
 
@@ -76,6 +77,11 @@ export const featureConfig: Record<
     minimumVersion: undefined,
     defaultValue: false,
   },
+  [Feature.ScalingReservedRam]: {
+    envVar: "CODEQL_ACTION_SCALING_RESERVED_RAM",
+    minimumVersion: undefined,
+    defaultValue: false,
+  },
   [Feature.UploadFailedSarifEnabled]: {
     envVar: "CODEQL_ACTION_UPLOAD_FAILED_SARIF",
     minimumVersion: "2.11.3",