Add "PA" to valid sample_id in the sample metadata & tissue_id in assay metadata

[cebriggs7135]

PA is pancreas, a new organ type. Please add this to constraint "pattern" for both sample_id and tissueid. Currently, only these are allowed: "([A-Z]+[0-9]+)-(BL|BR|LB|RB|HT|LK|RK|LI|LV|LL|RL|LY\d\d|SI|SP|TH|TR|UR|OT)(-\d+)+(\d+)?"

• Does this change have buy-in from other groups providing the same kind of data?
• Can you quote or reference any outside documentation that motivates this change?
• Is this change backward compatible, or does it make validation more stringent?

@cebriggs7135 will evaluate this request, and if it can move forward, will file a PR for @ngehlenborg to review, and @mccalluc will make sure tests pass before merging.

[mccalluc]

@cebriggs7135 : Looking in to this, this regex has already been simplified in all_assays.yaml:

  constraints:
    pattern: '([A-Z]+[0-9]+)-[A-Z]{2}\d*(-\d+)+(_\d+)?'

I don't think there is any argument for Sample to be different from Dataset.