Feature Request: Allow an optional path to be included in the destination URL for an InfluxDB subscription.

Currently Kapacitor allows the user to control the scheme, domain name and port of the InfluxDB subscription URL via the various configuration options, however, it does not provide the ability to include a path portion of the subscription URL for InfluxDB. This path portion is necessary if your kapacitor is sitting behind a certain path behind a reverse proxy.

Start by locating the InfluxDB subscription URL construction and the existing configuration options for scheme, domain, and port. Add support for an optional path and verify that the resulting destination URL can address Kapacitor behind a reverse proxy path.

Written by the indexing model from the issue text.