Accept an arbitrary path to /migrations in config

[PSalant726]

Purpose

PyPI installs the fidesops /migrations directory outside of the package source tree, in a sibling directory of /fidesops. This enables a way to specify a path to DB migrations that exists outside of the /fidesops package source tree.

Changes

• config.package.PATH --> config.package.MIGRATION_PATH
• If provided, fidesops does not prescribe the directory structure within the MIGRATIONS_PATH, other than that a /migrations directory must exist
• Dramatically reduce the os package import volume in config.py

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 #612

[sanders41]

This looks good to me. Should we wait to merge while we discuss #612 since the decision there may change this?

[PSalant726]

Closing in favor of #615 and a resulting PR, re: #612 (comment).