Create finished audit log for privacy requests

[TheAndrewJackson]

Purpose

Add AuditLog for finished requests so users can easily see when they're done.

Changes

• Update fideslib and fix small issue with with a case change. ENCODING -> encoding
• New migration adding another enum option to support the updated AuditLogAction
• Create AuditLog when a subject request finishes

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
• Applicable documentation updated (guides, quickstart, postman collections, tutorial, fidesdemo, database diagram.
• If docs updated (select one):
  • 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 #1022

[seanpreston]

Something that would be nice here is to wrap this new AuditLog creation into a transaction with privacy_request.save(...) — if one of these operations fails without the other we'd end up with an incomplete state, so it's better to commit them both at once.

[TheAndrewJackson]

Good find. That is a potential issue when approved/denied are created as well. All of the audit logs should probably be updated at the same time when this is done.

Would you like this to be addressed in this PR or a follow up?

[seanpreston]

Let's do it as a follow-up