feat: Create .gitattributes in aztec-nr (#2661)

This will make it easier to read contracts in the aztec.nr with Rust
syntax highlighting. This can be reverted once Github officially
supports Noir syntax highlighting.

# Checklist:
Remove the checklist to signal you've completed it. Enable auto-merge if
the PR is ready to merge.
- [ ] If the pull request requires a cryptography review (e.g.
cryptographic algorithm implementations) I have added the 'crypto' tag.
- [x] I have reviewed my diff in github, line by line and removed
unexpected formatting changes, testing logs, or commented-out code.
- [x] Every change is related to the PR description.
- [ ] I have
[linked](https://docs.github.com/en/issues/tracking-your-work-with-issues/linking-a-pull-request-to-an-issue)
this pull request to relevant issues (if any exist).

yarn-project/aztec-nr/.gitattributes

@@ -0,0 +1 @@
+*.nr linguist-language=Rust