Allow for multiple `is_default` templates / Set `is_default = true` for "Alliance Simplified..." template

[aaronskiba]

Description

DMP Assistant currently only has one default template ("Alliance Template").

• The "Alliance Template" and "Alliance Simplified Template (Funding Application Stage)" comprise the "priority templates" that populate the templates dropdown. It might make sense to also set the "Alliance Simplified Template (Funding Application Stage)" as a default template.
  • One advantage, is that it would strengthen the current code used to populate the templates dropdown:

  # app/controllers/template_options_controller.rb
  
  # Returns a JSON payload with the following structure:
  # - templates:
  #   - org_templates: [All non-funder templates]
  #   - priority_templates: [The simplified and default funder templates]
  #   - other_templates: [All non-priority funder templates]
  # - total_templates: Count of all templates
  def build_templates_payload(templates)
    funder_templates = templates.select { |t| t.org_id == DEFAULT_FUNDER_ID }
    simplified = funder_templates.find { |t| t.title == _('Alliance Simplified Template (Funding Application Stage)') }
    default = funder_templates.find(&:is_default)
    priority_templates = [simplified, default].compact
  
    { templates: { org_templates: templates - funder_templates,
                   priority_templates: priority_templates,
                   other_templates: funder_templates - priority_templates },
      total_templates: templates.size }
  end

  The issue with the above code, is that unwanted behaviour will be encountered if 'Alliance Simplified Template (Funding Application Stage)' is ever renamed.

Proposed Solution

Update the codebase to allow for multiple templates where is_default == true and set template.is_default = true for the 'Alliance Simplified Template (Funding Application Stage)' template.
From there the above code be simplified and strengthened (e.g. priority_templates = funder_templates.select(&:is_default))

[aaronskiba]

# app/models/template.rb

  def self.default
    where(is_default: true, published: true).last
  end

Looking at the above code, it might even be the case that the app is only meant to have one default template? If so, we might be able to strengthen the aforementioned "Alliance Simplified..." template code by using the .customization_of or .family_id values.

Also, if the above is true, then could it even be the case that the "Alliance Simplified..." template rather than the "Alliance Template" should be the default template?