refactor(django): import from psycopg2 lazily

[P403n1x87]

Description

This change refactors the django patch module to avoid cross-importing from the psycopg2 integration, which might cause psycopg2 to be loaded, when available, even if not required by the traced application.

Checklist

• [x] Title must conform to conventional commit.
• [x] Add additional sections for feat and fix pull requests.
• [x] Ensure tests are passing for affected code.
• [x] Library documentation and/or Datadog's documentation site is updated. Link to doc PR in description.

Reviewer Checklist

• [x] Title is accurate.
• [x] Description motivates each change.
• [x] No unnecessary changes were introduced in this PR.
• [x] PR cannot be broken up into smaller PRs.
• [x] Avoid breaking API changes unless absolutely necessary.
• [x] Tests provided or description of manual testing performed is included in the code or PR.
• [x] Release note has been added for fixes and features, or else changelog/no-changelog label added.
• [x] All relevant GitHub issues are correctly linked.
• [x] Backports are identified and tagged with Mergifyio.
• [x] Add to milestone.