Provide generic issue/pr template in custom path

[camlafit]

Feature Description

As explaine more or less explained at https://docs.gitea.com/usage/issue-pull-request-templates we can't provide generic template for all instance.
To wait we have an PR to be more accurate about this limitation : #29035

Could be interesting as asked at https://forum.gitea.com/t/issue-template-directory/3328 to provide a generic template directory in custom path.

Thanks a lot

Screenshots

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