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/api-client.ts

@@ -3,8 +3,8 @@ import * as path from "path";
 import * as githubUtils from "@actions/github/lib/utils";
 import consoleLogLevel from "console-log-level";
 
-import { getMode, getRequiredEnvParam, getRequiredInput } from "./actions-util";
-import { isLocalRun } from "./util";
+import { getRequiredInput } from "./actions-util";
+import { getMode, getRequiredEnvParam, isLocalRun } from "./util";
 
 // eslint-disable-next-line import/no-commonjs
 const pkg = require("../package.json");
@@ -40,7 +40,7 @@ export const getApiClient = function (
   return new githubUtils.GitHub(
     githubUtils.getOctokitOptions(auth, {
       baseUrl: getApiUrl(apiDetails.url),
-      userAgent: `CodeQL ${getMode()}/${pkg.version}`,
+      userAgent: `CodeQL-${getMode()}/${pkg.version}`,
       log: consoleLogLevel({ level: "debug" }),
     })
   );