Include --expect-cells when using --aligner cellranger

[adairama]

Description of feature

As discussed in the Slack Channel for scrna-seq on 23rd September 2022:

It will be good to allow --expect-cells in the run with --aligner cellranger option for scrnaseq pipeline. Since the expected cells can vary between samples (e.g. 6000 for sample 1, 3000 for sample 2), it will be good have this as a column in the sample metadata.

Gregor Sturm suggested related issue:
#90 (comment)

[apeltzer]

CellRanger v.7 (which is included inthe pipeline) should auto-detect this btw, so actually not really needed. Not sure if its more accurate if we specify it (and what happens if we specify a wrong value here?).

[grst]

also universc should consume the expected_cells column. I suggest to add a value auto as default for cellranger.