DRY supported ssh key types

Add `Gitlab::SSHPublicKey.supported_types` method.
This method returns the names of ssh keys GitLab supports.
`Gitlab::SSHPublicKey` should be the source of truth about such
information.
`SUPPORTED_KEY_TYPES` has the same information so I reused the method
to prevent duplication that would allow easier to extend the list of
supported keys.
See https://gitlab.com/gitlab-org/gitlab/-/issues/213259.

app/models/application_setting_implementation.rb

@@ -14,7 +14,7 @@ module ApplicationSettingImplementation
   # Setting a key restriction to `-1` means that all keys of this type are
   # forbidden.
   FORBIDDEN_KEY_VALUE = KeyRestrictionValidator::FORBIDDEN
-  SUPPORTED_KEY_TYPES = %i[rsa dsa ecdsa ed25519].freeze
+  SUPPORTED_KEY_TYPES = Gitlab::SSHPublicKey.supported_types
   VALID_RUNNER_REGISTRAR_TYPES = %w(project group).freeze
 
   DEFAULT_PROTECTED_PATHS = [

lib/gitlab/ssh_public_key.rb

@@ -19,6 +19,10 @@ module Gitlab
       TECHNOLOGIES.find { |tech| key.is_a?(tech.key_class) }
     end
 
+    def self.supported_types
+      TECHNOLOGIES.map(&:name)
+    end
+
     def self.supported_sizes(name)
       technology(name)&.supported_sizes
     end

spec/lib/gitlab/ssh_public_key_spec.rb

@@ -21,6 +21,14 @@ RSpec.describe Gitlab::SSHPublicKey, lib: true do
     end
   end
 
+  describe '.supported_types' do
+    it 'returns array with the names of supported technologies' do
+      expect(described_class.supported_types).to eq(
+        [:rsa, :dsa, :ecdsa, :ed25519]
+      )
+    end
+  end
+
   describe '.supported_sizes(name)' do
     where(:name, :sizes) do
       [

spec/models/application_setting_spec.rb

@@ -491,7 +491,7 @@ RSpec.describe ApplicationSetting do
 
     context 'key restrictions' do
       it 'supports all key types' do
-        expect(described_class::SUPPORTED_KEY_TYPES).to contain_exactly(:rsa, :dsa, :ecdsa, :ed25519)
+        expect(described_class::SUPPORTED_KEY_TYPES).to eq(Gitlab::SSHPublicKey.supported_types)
       end
 
       it 'does not allow all key types to be disabled' do