Allow to disable any addon in the addon settings.

[domingo2000]

Motivation

Closes #3418

Implementation

In addon loading check for the addon settings first. The addon can be disabled using

"rubyLsp.addonSettings": {
    "RuboCop": {
      "enabled": false
    }
  }

We make the addons enabled by default.

Automated Tests

Added tests when the addon is enabled and when the addon is disabled. The other tests are already testing if the setting is not set.

Manual Tests

Tests in the same repo enabling/disabling a dummy addon.

Screencast.from.21-05-25.22.27.12.webm

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[domingo2000]

I can also write some documentation for this if needed. Just let me know where it should go and what kind of UX writing would work best. 📝