Adjust code, headers, and vignette for required/not required arguments

[kweav]

The changes in this PR address requiring the cell_line argument for gimap_annotate() and clarifying pg_metadata/sample_metadata (which one is required/used) for setup_data().

For the cell_line argument:

• I removed the default value
• Explained in the header that it is required
• added providing its value to the headers for this and all subsequent functions
• Provided more clarity in the vignette about providing it
• Also included a toupper() when utilizing the argument to filter the DepMap data since the stripped cell line column appears to have capitalized cell lines upon inspection.

For the pg_metadata argument:

• I removed the argument from documentation, code, and the test function as it's not used and certainly was not required.

For the sample_metadata argument:

• I made it a required argument such that if it's not provided the NULL default will trigger the program to stop and make the user provide it since it's necessary for later steps.
• I tried to clarify the description of this in the vignette.

[cansavvy]

This is great! Let's merge it. Between this and a little thing I added over on #57 I think this will cover it!