Handle unreliable gocql close function stuck issue

[wxing1292]

What changed?

• Start a new goroutine when closing gocql session

Why?
gocql session.Close is not reliable, sometimes there can be deadlock issue, details see below

1. stack trace proving that gocql session.Close is stuck

goroutine 700966 [chan send, 61 minutes]:
github.com/gocql/gocql.(*controlConn).close(0xc0026b8c80)
	/go/pkg/mod/github.com/gocql/gocql@v0.0.0-20210621133426-d83b80dfb480/control.go:488 +0xbb
github.com/gocql/gocql.(*Session).Close(0xc0015c2a80)
	/go/pkg/mod/github.com/gocql/gocql@v0.0.0-20210621133426-d83b80dfb480/session.go:464 +0x15f
go.temporal.io/server/common/persistence/nosql/nosqlplugin/cassandra/gocql.(*session).refresh(0xc001daeb60)
	/go/pkg/mod/go.temporal.io/server@v1.11.1-0.20210801055905-ea5caf1c1ea1/common/persistence/nosql/nosqlplugin/cassandra/gocql/session.go:107 +0x5cd
go.temporal.io/server/common/persistence/nosql/nosqlplugin/cassandra/gocql.(*query).handleError(...)
	/go/pkg/mod/go.temporal.io/server@v1.11.1-0.20210801055905-ea5caf1c1ea1/common/persistence/nosql/nosqlplugin/cassandra/gocql/query.go:133

2. call stack which triggered the above deadlock (from caller to callee)
   a. https://github.com/gocql/gocql/blob/d83b80dfb4800e8761487e2a0c86cf6864824a8e/session.go#L464
   b. https://github.com/gocql/gocql/blob/d83b80dfb4800e8761487e2a0c86cf6864824a8e/control.go#L488

How did you test it?
N/A

Potential risks
N/A

Is hotfix candidate?
No