Add a self-update command to the CLI

[hierynomus]

As a customer, I want to be able to update the CLI, so that I can take advantage of all the newest features

Problem

Currently there is no (easy) way described/available to update the new StackState CLI. This leads to questions from customers on how to update the CLI, or which version they need.

Solution

Implement an sts update command that checks whether the latest version of the CLI is installed and if not installs it.

The command should support the following flags:

• --dry-run – Only check whether a new version is available

The output of the command should be:

New version	Dry-run	JSON	Text
✅	❌	{ "version": "<new>", "latest": false, "upgraded": true }	Upgraded to version '<new>'
✅	✅	{ "version": "<new>", "latest": false, "upgraded": false }	Newer version '<new>' is available
❌	❌	{ "version": "<current>", "latest": true, "upgraded": false }	You're running the latest version
❌	✅	{ "version": "<current>", "latest": true, "upgraded": false }	You're running the latest version

Implementation

A nice framework/library for building this might be https://github.com/mouuff/go-rocket-update , which allows to implement a provider to check our S3 bucket for the latest version and download from there.

[rogerniesten]

Please take into account that not all servers can directly access the internet (so the StackState download servers), but need a proxy for that. So my suggestion is to add an option --proxy which enables the possibility to specify a proxy server.
Examples

-- proxy http://proxy.company.com
-- proxy http://proxy.company.com:1234
-- proxy http://user:password@proxy.company.com:1234