Explain Privacy Request Execution [#1397]

[pattisdr]

Purpose

We have guides talking about how to configure Fidesops but we're missing a high-level explanation of how Privacy Request Execution works.

Changes

• Add a Fidesops Privacy Request Execution page to the docs
• Clarify how authentication is setup for Policy Webhooks

Checklist

• [ ] Update CHANGELOG.md file
  • [ ] Merge in main so the most recent CHANGELOG.md file is being appended to
  • [ ] Add description within the Unreleased section in an appropriate category. Add a new category from the list at the top of the file if the needed one isn't already there.
  • [ ] Add a link to this PR at the end of the description with the PR number as the text. example: #1
• [X] Applicable documentation updated (guides, quickstart, postman collections, tutorial, fidesdemo, database diagram.
• If docs updated (select one):
  • [X] documentation complete, or draft/outline provided (tag docs-team to complete/review on this branch)
  • [ ] documentation issue created (tag docs-team to complete issue separately)
• [ ] Good unit test/integration test coverage
• [ ] This PR contains a DB migration. If checked, the reviewer should confirm with the author that the down_revision correctly references the previous migration before merging
• [ ] The Run Unsafe PR Checks label has been applied, and checks have passed, if this PR touches any external services

Ticket

Fixes #1397

[pattisdr]

@conceptualshark, @ethyca/docs-authors Sean asked me to take a stab at a first draft of how Privacy Request Execution works, for the guides, separate from how we configure Fidesops.

[conceptualshark]

🙏 Thank you for the proofread! Should be all set.