Improve UX for metadata module

[Lilly-May]

Description of feature

The methods in the metadata module would benefit from revision, especially regarding the parameters. In some cases, the parameter inference and default settings could be improved or, at least, better documented.

Two specific things discussed in scverse/pertpy-tutorials#48:

• In CellLine.annotate_bulk_rna, the reference_id is implicitly set to DepMap_ID, and a warning is raised to inform the user of the steps to take if that column is not present. This process could be improved by explicitly checking whether DepMap_ID is available in adata.obs and, if it is not, raising an error (or a warning). (see code here)
• In CellLine.correlate, we check if the gene names are different and issue a warning if they are. We should discuss whether it makes more sense to let the method to fail if the names do not match. If not, the warning should at least clarify the implications of this discrepancy. (see code here)