feat: add analytics (#819)

* feat: add analytics

This feature adds the AnalyticsHandler class to manage opt-in/opt-out and
tracking of events happening within the CLI and the Dashboard.
Introduces also the command `garden config analytics-enabled` to update your
preferences.

* docs: strip ANSI characters out of command descriptions

docs/reference/commands.md

@@ -17,10 +17,10 @@ The following option flags can be used with any of the CLI commands:
   | `--silent` | `-s` | boolean | Suppress log output. Same as setting --logger-type=quiet.
   | `--env` | `-e` | string | The environment (and optionally namespace) to work against.
   | `--logger-type` |  | `quiet` `basic` `fancy` `json`  | Set logger type.
-[1mfancy:[22m updates log lines in-place when their status changes (e.g. when tasks complete),
-[1mbasic:[22m appends a new log line when a log line's status changes,
-[1mjson:[22m same as basic, but renders log lines as JSON,
-[1mquiet:[22m suppresses all log output, same as --silent.
+fancy: updates log lines in-place when their status changes (e.g. when tasks complete),
+basic: appends a new log line when a log line's status changes,
+json: same as basic, but renders log lines as JSON,
+quiet: suppresses all log output, same as --silent.
   | `--log-level` | `-l` | `error` `warn` `info` `verbose` `debug` `silly` `0` `1` `2` `3` `4` `5`  | Set logger level. Values can be either string or numeric and are prioritized from 0 to 5 (highest to lowest) as follows: error: 0, warn: 1, info: 2, verbose: 3, debug: 4, silly: 5.
   | `--output` | `-o` | `json` `yaml`  | Output command result in specified format (note: disables progress logging and interactive functionality).
   | `--emoji` |  | boolean | Enable emoji in output (defaults to true if the environment supports it).
@@ -808,3 +808,31 @@ Throws an error and exits with code 1 if something's not right in your garden.ym
 
     garden validate 
 
+### garden config analytics-enabled
+
+Update your preferences regarding analytics.
+
+To help us make Garden better, you can opt in to the collection of usage data.
+We make sure all the data collected is anonymized and stripped of sensitive
+information. We collect data about which commands are run, what tasks they trigger,
+which API calls are made to your local Garden server, as well as some info
+about the environment in which Garden runs.
+
+You will be asked if you want to opt-in when running Garden for the
+first time and you can use this command to update your preferences later.
+
+Examples:
+
+    garden config analytics-enabled true   # enable analytics
+    garden config analytics-enabled false  # disable analytics
+
+##### Usage
+
+    garden config analytics-enabled [enable] 
+
+##### Arguments
+
+| Argument | Required | Description |
+| -------- | -------- | ----------- |
+  | `enable` | No | Enable analytics. Defaults to "true"
+