🐛 changes for molecular validation docs

[rosibaj]

• make this order consistent
  
• fix this wording:

For paired-end sequencing, file_r1 and file_r2 must not be the same file.  
--->  
For a given submitter_read_group_id, if providing paired-end FASTQ files, file_r1 and file_r2 must not be the same file. However, for paired-end BAM files, file_r1 and file_r2 must be the same file.

• Fix this wording: #398 (comment)
  "file_r2": "test_rg4.bam" ---> "file_r2": "test_rg3.bam"

• Fix this wording: #398 (comment)
  "file_r2": "test_rg4.bam" ---> "file_r2": "test_rg3.bam"

• All changes from here: #402 (review)