fix(template): Use env variable USERNAME in Windows

[Nekketsu]

Summary

When creating capturing templates we can un the %n variable to insert the current user. It is done by using the environment variable USER. However, in Windows the variable is called USERNAME. This PR fixes this issue.

This PR adds..

Related Issues

Related #

Closes #

Changes

• Check whether it is being run in Windows.
• If is running in Windows it uses the environment variable USERNAME to query the current user name, otherwise it uses the USER variable.

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
• Checked for breaking changes and documented them, if any.

[kristijanhusak]

Thanks!