Custom file templates in the Web IDE
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=214406)
</details>
<!--IssueSummary end-->
### Problem to solve
When I am writing a release post item, I need to create a new file and copy and paste from the template file. I want to be able to easily create a file in the appropriate directory from a simple template.
### Further details
### Proposal
When I am in the Web IDE, I should be able to:
- Create a new file
- Select a custom project file template type (e.g. "Release post item")
- Select a template within the template type (e.g. "Primary")
- The Web IDE should suggest the correct directory, so that all I need to do it provide a file name.
This would also be useful for blog posts, and other kinds of content too.
### Links / references
issue