Add support for Mistral 7B

[rmitsch]

Description

Add support for Mistral 7B.
Note: this requires transformers>=4.33.4, which hasn't been released at the time of writing (2023-10-03) to run without installing from source.

Corresponding documentation PR

explosion/spaCy#13037

Types of change

New feature.

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran all tests in tests and usage_examples/tests, and all new and existing tests passed. This includes
  • all external tests (i. e. pytest ran with --external)
  • all tests requiring a GPU (i. e. pytest ran with --gpu)
• My changes don't require a change to the documentation, or if they do, I've added all required information.