Add support for customizable precedence in Settings Module

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MR: Pending

Description

Add support for customizable precedence in Settings Module.

There may be cases where we want different settings in the settings module to have different precedence rules, and rather than be stuck with a one-size-fits-all, lets go ahead and add support for making the precedence rules configurable on a per-setting basis.

This will have the additional benefit of further abstracting/standardizing the existing support for determining "relevant settings" for a given step, which currently relies on manual per-step logic and guard clauses.

See related discussion in this thread.

• See Workspaces Settings Configuration Infrastructur... (&14186) for overview and more context
• See Related Issues and MRs section in that epic for related issues and MRs

Acceptance Criteria

• Precedence rules can be configured on a per-setting basis

Technical Requirements

Here is an initial idea of what this API might look like:

module RemoteDevelopment
  module Settings
    class DefaultSettings
      def self.default_settings
        {
          some_setting: {
            default_value: 1,
            type: Integer,
            sources: [SomeSettingsReader, SomeOtherSettingsReader]
          },
          # ...
        }
      end
    end
  end
end

module RemoteDevelopment
  module Settings
    class SomeSettingsReader
      def self.read(context)
        err_result = nil

        SettingsBuilder.provide_settings_values(step_class: self, context: context) do |setting_name, values_from_previous_steps|
          # NOTE: values_from_previous_steps can be used if this step needs to know the values of other settings

          begin
            ClassToReadSomeSetting.read(setting_name) # read and return setting value from some source, to contribute to context
          rescue
            err_result = Gitlab::Fp::Result.err(SettingsSomeSettingsReadFailed.new(details: "Some failure for #{setting_name}"))
            break
          end

          # provide_settings_values will take the returned setting value, and add it to the list of "contributed" settings
        end

        return err_result if err_result

        Gitlab::Fp::Result.ok(context)
      end
    end
  end
end

module RemoteDevelopment
  module Settings
    class SettingsPrecedenceSorter # last step in the Settings Module ROP chain
      def self.sort(context)
        context[:settings] = SettingsBuilder.sort(context) # sort out the settings based on order of sources

        context
      end
    end
  end
end

Design Requirements

None, no UI changes.