Support Dgraph4 connection string

[EnricoMi]

Checklist before submitting

• Did you read the contributing guide?
• Did you update the docs?
• Did you write any tests to validate this change?

Description

Fixes # (issue).

Review process for approval

1. All tests and other checks must succeed.
2. At least one core contributors must review and approve.
3. If a core contributor requests changes, they must be addressed.

[github-actions]

Test Results

 3 180 files   3 180 suites   52m 24s ⏱️
   440 tests    438 ✅ 0 💤   2 ❌
46 640 runs  46 428 ✅ 0 💤 212 ❌

For more details on these failures, see this check.

Results for commit 4e7a5df.

♻️ This comment has been updated with latest results.