Closes #3839

Closes #3811

Introducing the curl bug bounty program on hackerone. We now recommend
filing security issues directly in the hackerone ticket system which
only is readable to curl security team members.

Assisted-by: Daniel Gustafsson

Closes #3488

This backpedals back the documents to the state before bountygraph.

Closes #3311

Retract the previous approach as the sponsors will be the ones to set the
final amounts.

Closes #3152
[ci skip]

[ci skip]

Bug bounty explainer. See https://bountygraph.com/programs/curl

Closes #3067