Add injection schema

[kushalbakshi]

This PR adds injection schema - tables related to viral injections (AAV, RSV, etc.) in the brain. In the current design, the injection schema contains tables with foreign keys to tables in the surgery schema, requiring the surgery module to be activated first.

Before merging, the following will need to be addressed and resolved:

• Currently, the surgery module contains a table for Implantation which refers to an implantation surgery. Since a viral injection can be an independent surgery from an implant, a table redesign is likely necessary. A suggested redesign of the surgery module could take the form of: adding a Lookup table SurgeryType with options for Implant, ViralInjection, Implant + ViralInjection, and a downstream Surgery table containing the SurgeryType table as one of its attributes.
• Add docstrings to new tables.
• Add / update documentation for the new tables and any table redesign.
• Apply Black formatting
• Update version.py
• Update CHANGELOG

[kabilar]

Thanks @kushalbakshi! Please see my comments above, and please update the docs (with a dj.Diagram and API docs table) and docstrings.

all requested changes have been addressed