fix(webui): set sane timeout for get_instances_data calls

Summary

• fix(http_server): consider timeout for establishin TCP connections in HTTP server

Due to the bug in RPC (see #991) RPC call timeout does not account TCP connection establishment. So a request to a peer without a connection was not aborted due to timeout. Force a timeout directly for a future returned by RPC to avoid this

Closes #991

• fix(webui): set sane timeout for get_instances_data calls

Previously webUI failed to retrieve data about instances if one of those was dead. The cause was that webUI HTTP request timeout was less than get_instances_data timeout.

References #943 (closed)

• Close #...
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• Docs follow-up: not necessary