[CLN] Add gitattributes entry to mark generated files (#1231)

## Description of changes

*Summarize the changes made by this PR.*
 - Improvements & Bug fixes
- Edit .gitattributes to collapse generated files
(https://thoughtbot.com/blog/github-diff-supression)
 - New functionality
	 - ...

## Test plan
*How are these changes tested?*

- [x] Tests pass locally with `pytest` for python, `yarn test` for js

## Documentation Changes
*Are all docstrings for user-facing APIs updated if required? Do we need
to make documentation changes in the [docs
repository](https://github.com/chroma-core/docs)?
None required*

.gitattributes

@@ -0,0 +1 @@
+*_pb2.py* linguist-generated