MINOR: connection: extend takeover with release option

MINOR: connection: extend takeover with release option

Extend takeover API both for MUX and XPRT with a new boolean argument
<release>. Its purpose is to signal if the connection will be freed
immediately after the takeover, rendering new resources allocation
unnecessary.

For the moment, release argument is always false. However, it will be
set to true on delete server CLI handler to proactively close server
idle connections.