Add environment variables to signal feature and version to the CLI

This PR ensures environment variables are set before any invocation of
the CLI.  Here is a list of vars that are set:

https://github.com/github/codeql-coreql-team/issues/1124#issuecomment-852463521

This ensures the CLI knows the features and versions of the containing
actions/runner.

Additionally:

- Fix the user agent so that it more closely aligns with user agent
  spec
- Refactor environment variable initialization so that it all happens in
  one place and call.
- Move Mode, getRequiredEnvParam, setMode, getMode out of actions-util
  and into util. actions-util is meant for utils only called by the
  action, not the runner.

The `prepareLocalRunEnvironment()` method is most likely deprecated and
should be removed. I originally added it because I had a way of working
where I would run the action from my local machine to test out changes,
but this was always a little flaky. So, I no longer use this way of
working. I will probably remove it soon.

src/util.test.ts

@@ -9,6 +9,7 @@ import sinon from "sinon";
 import * as api from "./api-client";
 import { getRunnerLogger, Logger } from "./logging";
 import { setupTests } from "./testing-utils";
+import { initializeEnvironment, Mode } from "./util";
 import * as util from "./util";
 
 setupTests(test);
@@ -77,6 +78,8 @@ test("getThreadsFlag() throws if the threads input is not an integer", (t) => {
 });
 
 test("isLocalRun() runs correctly", (t) => {
+  initializeEnvironment(Mode.actions, "1.2.3");
+
   process.env.CODEQL_LOCAL_RUN = "";
   t.assert(!util.isLocalRun());
 
@@ -91,6 +94,9 @@ test("isLocalRun() runs correctly", (t) => {
 
   process.env.CODEQL_LOCAL_RUN = "hucairz";
   t.assert(util.isLocalRun());
+
+  initializeEnvironment(Mode.runner, "1.2.3");
+  t.assert(!util.isLocalRun());
 });
 
 test("getExtraOptionsEnvParam() succeeds on valid JSON with invalid options (for now)", (t) => {