Otter-grader

* Update Otter Grade image tag when the base image changes per [583](https://github.com/ucbds-infra/otter-grader/issues/583)
* Make gspread an optional dependency per [577](https://github.com/ucbds-infra/otter-grader/issues/577)

* Added configuration files for Otter Assign per [565](https://github.com/ucbds-infra/otter-grader/issues/565)
* Fixed log execution bug from Slack as described in [571](https://github.com/ucbds-infra/otter-grader/pull/571)

* Added `ipython` to `install_requires`

* Added `MANIFEST.in`

* Display emojis with test results to more clearly show which tests pass and which fail, as per [533](https://github.com/ucbds-infra/otter-grader/pull/533).
* Allow users to specify a Python version in Otter Generate and Otter Assign
* Round `results.json` point values to 5 decimal places per [538](https://github.com/ucbds-infra/otter-grader/issues/538)
* Optionally display PDF generation/submission failures to students via `results.json` per [494](https://github.com/ucbds-infra/otter-grader/issues/494)
* Added the `force_public_test_summary` key to the autograder config per [539](https://github.com/ucbds-infra/otter-grader/issues/539)
* Made the "Public Tests" section on Gradescope appear as failing when not all public tests passed per [539](https://github.com/ucbds-infra/otter-grader/issues/539)

* Close temporary file handle before removal when checking tests in `otter.Notebook.export`
* Fixed bug caused by unspecified encoding in Windows JSON loads per [524](https://github.com/ucbds-infra/otter-grader/issues/524)
* Updated autograder zip `setup.sh` file and `r-base` version per [514](https://github.com/ucbds-infra/otter-grader/issues/514)
* Fix point value filtering for student tests in Otter Assign per [503](https://github.com/ucbds-infra/otter-grader/issues/503)