Remove ".git" suffix when creating a repository

[minwoox]

To simplify the operation that uses the repository name such as the authorization system.
GitHub also removes the suffix automatically when creating a repository.

[ikhoon]

I slightly prefer rejecting a repo name ending with .git instead of an automatic strip.

[minwoox]

Alright, it's time to vote. @line/dx

For the record, GitHub just removes the suffix.

[minwoox]

On second thought, I also prefer rejecting it because we might change the underlying database from Git to another.
But please let me know if you have any other opinions.