ringhash: add logs to surface information about ring creation

[easwars]

The newly added logs like this:

ring.go:70 [xds] [ring-hash-lb 0xc000148080] newRing: number of subConns is 1, minRingSize is 1024, maxRingSize is 4096  (t=+3.468892ms)
ring.go:74 [xds] [ring-hash-lb 0xc000148080] newRing: normalized subConn weights is [{0xc0001145a0 1}]  (t=+3.485234ms)
ring.go:85 [xds] [ring-hash-lb 0xc000148080] newRing: creating new ring of size 1024  (t=+3.497625ms)

Fixes #5781

RELEASE NOTES: none