MDL-61899 tool_dataprivacy: Subject access requests tool

This commit is composed of different issues, most of them under
MDL-61306:
- MDL-61888, MDL-61785, MDL-61830, MDL-61874, MDL-59720,
  MDL-61486, MDL-61697, MDL-61798, MDL-61685, MDL-61682,
  MDL-61684, MDL-61618, MDL-61681, MDL-61680, MDL-61487,
  MDL-61499, MDL-61500, MDL-61362 and MDL-59718

Contributions to this patch by:
- Jun Pataleta
- David Monllao
- Andrew Nicols
- Adrian B. Greeve
- Jake Dallimore
- Sara Arjona