[BulkRNASeq] Handle processing with experimental groups where N = 1

[J-81]

Description

Certain datasets have experimental groups of single samples.
This current breaks differential expression approaches and likely means differential expression will be impossible.

Steps to Reproduce

1. Create subset of Runsheet rows with at least one group with N = 1 samples

Expected Behavior

Processing workflows should identify these cases and process up to DE but not run DE.
In these cases, normalized data should be available for release.

Actual Behavior

Processing attempts DE and raises exception.

Impact on Data

Non silent bug: no processed data released with this causing an issue.
Known to impact 1 dataset at start of this issue.

Additional Context

Provide any additional information or context that might be relevant to the issue.

Possible Solution (optional)

Process through normalization, then stop.
This will require some modification for post processing which assumes complete processing.