Add P3A questions for Top Level Domain Blocking

[pes10k]

Follow up / related to top level domain blocking: #14134

To get a better understanding of how often folks are using top level domain blocking, and what choices they're making when presented with it, the feature should include the following P3A questions:

1. How many times the user encountered a top level domain blocking prompt in the last week:
   • 0
   • 1-5
   • 5-10
   • 10-50
   • more than 50
2. How the user responded to the P3A prompt (privacy protection: randomized response, so X% report true value, 1-X report an answer at random)
   • did nothing (ie closed tab or similar)
   • clicked "go back"
   • clicked "proceed"
   • clicked "proceed" and "remember my choice"

[pes10k]

@moritzhaller I wasn't sure what the P3A randomized response rate was, could you remind what X is in current P3A when you have a moment?