Data provider simplification, tests, and documentation (#1997)

* Ignore env.test from source control

* Simplification of providers interface

* Synth tests

* Update money to use new find rates method

* Remove unused issues code

* Additional issue feature removals

* Update price data fetching and tests

* Update documentation for providers

* Security test fixes

* Fix self host test

* Update synth usage data access

* Remove AI pr schema changes

app/models/providers.rb

@@ -0,0 +1,35 @@
+module Providers
+  module_function
+
+  def synth
+    api_key = ENV.fetch("SYNTH_API_KEY", Setting.synth_api_key)
+
+    return nil unless api_key.present?
+
+    Provider::Synth.new(api_key)
+  end
+
+  def plaid_us
+    config = Rails.application.config.plaid
+
+    return nil unless config.present?
+
+    Provider::Plaid.new(config, region: :us)
+  end
+
+  def plaid_eu
+    config = Rails.application.config.plaid_eu
+
+    return nil unless config.present?
+
+    Provider::Plaid.new(config, region: :eu)
+  end
+
+  def github
+    Provider::Github.new
+  end
+
+  def openai
+    # TODO: Placeholder for AI chat PR
+  end
+end