Selectively enable or disable instance level template inheritance for sub projects and groups
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### Release notes
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Setting an instance level issue template causes all sub groups and projects to inherit it. There is currently no flexibility to enable or disable this inheritance selectively for projects where the instance level templates are not applicable, leading to an undesirably cluttered and lengthy issue template list. This proposal is to allow for selectively disabling inheritance on a per project/group basis.
### Problem to solve
When a template repository is defined at the instance level, there is no way for a new project to prevent template inheritance.
This is problematic for specific projects where the instance template file does not match the needs.
The instance level template (eg: issue template) still appears in the dropdown menu and can unnecessarily clutter the template list, leading to user confusion.
### Proposal
Add a checkbox (ticked by default) in the project creation view and settings that allows to disable instance level template inheritance.
### Intended users
* [Parker (Product Manager)](https://handbook.gitlab.com/handbook/product/personas/#parker-product-manager)
* [Delaney (Development Team Lead)](https://handbook.gitlab.com/handbook/product/personas/#delaney-development-team-lead)
* [Presley (Product Designer)](https://handbook.gitlab.com/handbook/product/personas/#presley-product-designer)
* [Sasha (Software Developer)](https://handbook.gitlab.com/handbook/product/personas/#sasha-software-developer)
### Does this feature require an audit event?
No
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