Mux-python

- Remove `ad_watch_time` and `view_content_watch_time`, metrics which do not exist.

*Note:* The above change may be considered breaking; if you were accessing either field on a base Video View, that will no longer work. It is highly likely that your code was not using those fields, however. Additionally, those metrics are no longer allowed in the metrics API.

- Deprecate `encoding_tier` and add support for `video_quality` to replace it
- Add support for `premium` video quality
- Add support for updating `master_access` settings on Live Streams
- Add support for `view_dropped` and `view_dropped_percentage`

- support `video_quality` setting in place of deprecated `encoding_tier`. [Read more](https://www.mux.com/blog/no-one-said-naming-was-easy-encoding-tiers-are-now-video-quality-levels)
- add support for DRM. [Read more](https://www.mux.com/blog/introducing-drm-the-latest-tool-in-protecting-your-content-on-mux)

- prepare for upcoming feature release
- update docs around default measurement

- Add support for User Agent restrictions within `PlaybackRestriction`
- Add support for [error severity and business exceptions](https://docs.mux.com/guides/error-categorization)
- Add support for updated MP4 options
- Add support for [additional ad metrics](https://www.mux.com/blog/beyond-content-the-crucial-metrics-for-successful-ad-supported-streaming)
- Fix issue with handling generated subtitle tracks
- Add missing `encoding_tier` field to `DeliveryReport`

* Adds updated MP4 generation options.