default templates should allow to reference existing templates

Release notes

Improvement: reference existing templates for defining a default template

Problem to solve

Current used version: GitLab Enterprise Edition 15.2.2-ee

A company defines several merge request templates to use in a shared repository. This repository is configured as "template repository" on a group level (Group > Settings > General > Templates). When a new merge request is created the user could choose of one of the stored templates.

But the user always HAS to choose one. With default templates (Project > Settings > General > Merge requests > Default description template for merge requests | alternative default.md) you could define a default template to use. But you have to copy the content here.

Intended users

repository administrator
developer who creates a merge request, issue (wherelse default templates are used)

User experience goal

Developer could create a merge request without extra need to select a template.

Repository does not have to copy the default templates content to every project and therefore has DRY.

Proposal

Provide a way to reference an existing template.

Further details

nothing extra

Permissions and Security

unknown

Documentation

Availability & Testing

Available Tier

all tiers which provide default templates

Feature Usage Metrics

The new reference implies a new field. Setting this field could be measured.

What does success look like, and how can we measure that?

The setting of the 'old' field with default template content could also be measured, so you could see how many templates are migrated.