fix(balancer): respect max retries (#12346)

In the balancer phase, when obtaining a connection from the upstream
connection pool, the `cached` attribute of the peer connection is set
to 1(`pc->cached = 1;`), indicating that the connection is obtained
from the cache.

If an error occurs during the use of this connection, such as
"upstream prematurely closed connection" the system will increase the
`tries` attribute of the peer connection by executing
`u->peer.tries++`.

`tries` represents the maximum number of attempts to connect to an
upstream server. It is equal to the normal 1 attempt + `retries`
(default value is 5) = 6.
The occurrence of `u->peer.tries++` is unexpected and it results
in the actual retry count exceeding 6 in worst cases.

This PR restores tries by callbacks to the balancer when
`u->peer.tries++` is unexpectedly set.

FIX [FTI-5616](https://konghq.atlassian.net/browse/FTI-5616)

Signed-off-by: tzssangglass <[email protected]>