Remove trailing slash when reading configuration in the OnlyOffice connector

[shepilov]

It's also a big mystery we should put the URL with or without a trailing slash in the URL confirmation for the connector.

So it's better to remove all slashes from the configuration and internally use URLs starting from slash

[ericlinagora]

Most places I found remove any extraneous slashes before concatenating them, however the investigation revealed a series of other problems with the integration. I have not found a place where this was an issue, so marking as won't fix until more specific instructions for reproduction of the issue are added.