Add os.PathLike[str] type to ssl_ca_certs

[rnv812]

Summary

In Config class for parameter ssl_ca_certs we can actually add os.PathLike[str] type for compatibility with pathlib.Path instances.

There is only one place where self.ssl_ca_certs attribute is used - it is in load method in creating ssl context and its parameter ca_certs fully accept that type.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.