add celltype annotation functions

[ptajvar]

Adding functions and data to enable automated annotation of PBMC cells through label transfer from a reference dataset.

Fixes: PNA-2292 and PNA-2293

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

WIP

PR checklist:

• This comment contains a description of changes (with reason).
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• If a new tool or package is included, I have updated dependencies in pyproject.toml and cited it properly
• I have checked my code and documentation and corrected any misspellings
• I have documented any significant changes to the code in CHANGELOG.md