provide installMethod detail in server telemetry

config/config.example.js

@@ -276,4 +276,13 @@ module.exports = {
      *  (false by default)
      */
     verbose: false,
+
+    /*  Surplus information:
+     *
+     *  'installMethod' is included in server telemetry to voluntarily
+     *  indicate how many instances are using unofficial installation methods
+     *  such as Docker.
+     *
+     */
+    installMethod: 'unspecified',
 };

lib/env.js

@@ -20,6 +20,7 @@ var canonicalizeOrigin = function (s) {
 module.exports.create = function (config) {
     const Env = {
         version: Package.version,
+        installMethod: config.installMethod || undefined,
 
         httpUnsafeOrigin: canonicalizeOrigin(config.httpUnsafeOrigin),
         httpSafeOrigin: canonicalizeOrigin(config.httpSafeOrigin),

lib/stats.js

@@ -4,6 +4,7 @@ const Stats = module.exports;
 Stats.instanceData = function (Env) {
     var data = {
         version: Env.version,
+        installMethod: Env.installMethod,
 
         domain: Env.myDomain,
         subdomain: Env.mySubdomain,