(core) config: rename TEST_ENABLE_ACTIVATION to GRIST_FORCE_ENABLE_ENTERPRISE

Summary:
The name of this env var has bothered me for a little while.
Let's rename it more meaningfully.

Test Plan: No need to test, cosmetic change only.

Reviewers: jarek

Reviewed By: jarek

Differential Revision: https://phab.getgrist.com/D4320

app/server/lib/configCore.ts

@@ -25,7 +25,7 @@ export function loadGristCoreConfig(fileConfig?: FileConfig<IGristCoreConfigFile
   const fileConfigValue = fileConfigAccessorFactory(fileConfig);
   return {
     edition: createConfigValue<Edition>(
-      isAffirmative(process.env.TEST_ENABLE_ACTIVATION) ? "enterprise" : "core",
+      isAffirmative(process.env.GRIST_FORCE_ENABLE_ENTERPRISE) ? "enterprise" : "core",
       fileConfigValue("edition")
     )
   };