Tags::CreateService: add a handler for NoRepository exception

What does this MR do and why?

Contributes to #525296 (closed)

Problem

When provided tag information is incorrect, Gitaly returns a "Could not update refs/tags/%s. Please refresh and try again." error.

This error is not handled by Rails and causes a 500 error.

Solution

Add a handler for this exception and return a user-friendly error message instead.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Visit create new tag page
2. Try to create a tag with name (includes special symbols): test
3. You should see a human-friendly error

MR acceptance checklist

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