Resolves: https://github.com/spring-projects/spring-integration/issues/3199
Previously, the FCCF did not cache a shared connection; if server 1 is down
and server 2 is up, this caused an attempt to connect to server 1 every time
we got the connection.
Add 2 options: `refreshSharedInterval` and `closeOnRefresh`, defaulting to
0 and false respectively, to maintain the same behavior as before the options
existed.
Disallow caching of the single shared connection if the delegate factories are
`CachingClientConnectionFactory` instances.
**cherry-pick to 5.2.x**
I will backport to 5.1.x, 4.3.x after review/merge.
* Polish javadocs and fix typo in docs
fa0caeb1b4