Add tissue oxygen saturation St02 as a valid dataTypeLabel

[rob-luke]

Closes #125

[samuelpowell]

@rob-luke so will this automatically pass in the validator now it is in the MD?

[rob-luke]

Correct, or at least it should! We would probably want to add a test to the validator to ensure this is the case.

I also think it's ok if the spec leads the validator between version releases. I see a reasonable workflow as...

1. update made to spec and merged to main
2. tests added to validator to ensure it the new spec changes work with validator, changes made to validator if required
3. updated validator version released
4. updated spec version released

Within the governance model we have set up, the maintainers would do the merging in step 1, complete step 2 and 3, and then after the board and maintainers jointly agree on new spec version, the maintainers release a new spec. However, for now the board and maintainers are us, so we should remember to update the validator, thanks for highlighting this.

[samuelpowell]

Yes, this makes sense