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/runner.ts

@@ -4,7 +4,6 @@ import * as path from "path";
 
 import { Command } from "commander";
 
-import { Mode, setMode } from "./actions-util";
 import { runAnalyze } from "./analyze";
 import { determineAutobuildLanguage, runAutobuild } from "./autobuild";
 import { CodeQL, getCodeQL } from "./codeql";
@@ -22,6 +21,8 @@ import {
   getThreadsFlag,
   parseGitHubUrl,
   getGitHubAuth,
+  initializeEnvironment,
+  Mode,
 } from "./util";
 
 // eslint-disable-next-line import/no-commonjs
@@ -29,7 +30,7 @@ const pkg = require("../package.json");
 
 const program = new Command();
 program.version(pkg.version).hook("preAction", () => {
-  setMode(Mode.runner);
+  initializeEnvironment(Mode.runner, pkg.version);
 });
 
 function getTempDir(userInput: string | undefined): string {