Account Issue Model and Resolution Flow + Troubleshooting guides (#1090)

* Rough draft of issue system

* Simplify design

* Remove stale files from merge conflicts

* STI for issues

* Cleanup

* Improve Synth api key flow

* Stub api key for test

app/models/issue.rb

@@ -0,0 +1,35 @@
+class Issue < ApplicationRecord
+  belongs_to :issuable, polymorphic: true
+
+  after_initialize :set_default_severity
+
+  enum :severity, { critical: 1, error: 2, warning: 3, info: 4 }
+
+  validates :severity, presence: true
+
+  scope :active, -> { where(resolved_at: nil) }
+  scope :ordered, -> { order(:severity) }
+
+  def title
+    model_name.human
+  end
+
+  # The conditions that must be met for an issue to be fixed
+  def stale?
+    raise NotImplementedError, "#{self.class} must implement #{__method__}"
+  end
+
+  def resolve!
+    update!(resolved_at: Time.current)
+  end
+
+  def default_severity
+    :warning
+  end
+
+  private
+
+    def set_default_severity
+      self.severity ||= default_severity
+    end
+end