Introduced configurable path for certificate chain file in JsonRPCClient class

[JSydll]

I had a problem with connections to https remotes in a small project of mine and found the solution I propose here.

Of course, there is no test for this whatsoever (except me assuring that it works on my other project), but I don't know what the testing approach might look like here.

Also, I'm aware that the position of the newly introduced optional constructor parameter might break existing use cases, but I went for my intuition and would like to hear your opinion on that.