Allow insecure TLS client connections

[MarSchif]

Changes included in this PR

Feature: Allow insecure TLS client connections. Off by default, optionallay enabled via config option.

Current behavior

TLS certificates are validated with no option to skip validation e.g. for self-signed certificates.

New behavior

Option verify_cert for clients to skip TLS certificate validation (verify_cert is True by default). Aligns with "--insecure" options for curl, mosquitto and similar.

Impact

No impact on existing usage.

Checklist

1. Does your submission pass the existing tests?
2. Are there new tests that cover these additions/changes?
3. Have you linted your code locally before submission? -> No, the Unix specific pre-commit hooks (.sh) of this project do not work locally on my platform (Windows 11).