Placeholder for sensitive fields in DAST Site Profile Form

This is a follow up from !51583 (comment 521129769)

Problem Statement

We need to show a placeholder for sensitive fields while editing a DAST Site Profile form.

• Username (Text input)
• Password (Password input)
• Request headers (Text area)

Please note that request headers are optional

cc @annabeldunstone

Implementation Plan

• Consider request headers & password as sensitive fields (password is already being considered sensitive)
  • username shouldn't be sensitive
• Show a placeholder [Redacted] for sensitive fields
• Remove them the DAST profile summary
  • Remove it from the graphql query
  • Remove the summary cell
• Add specs to cover
  • sensitive fields
  • placeholder