Add option for clearing global normalClient dialer

[yaron12n]

Proposed changes

Cached normalClient might cause levelDB to be closed (If the engine was closed previously).
Adding an option for clearing it.

Checklist

• [x ] Pull request is created against the dev branch
• All checks passed (lint, unit/integration/regression tests etc.) with my changes
• I have added tests that prove my fix is effective or that my feature works
• [x ] I have added necessary documentation (if appropriate)

[dwisiswant0]

Any specific use case for this? Would be great if you could file an issue first.