New Features

gcp/observability: add support for Environment Variable GRPC_CONFIG_OBSERVABILITY_JSON (#5525)
gcp/observability: add support for custom tags (#5565)

Behavior Changes

server: reduce log level from Warning to Info for early connection establishment errors (#5524)
- Special Thanks: @jpkrohling

client: fix race in flow control that could lead to unexpected EOF errors (#5494)
client: fix a race that could cause RPCs to time out instead of failing more quickly with UNAVAILABLE (#5503)
client & server: fix a panic caused by passing a nil stats handler to grpc.WithStatsHandler or grpc.StatsHandler (#5543)
transport/server: fix a race that could cause a stray header to be sent (#5513)
balancer: give precedence to IDLE over TRANSIENT_FAILURE when aggregating connectivity state (#5473)
xds/xdsclient: request correct resource name when user specifies a new style resource name with empty authority (#5488)
xds/xdsclient: NACK endpoint resources with zero weight (#5560)
xds/xdsclient: fix bug that would reset resource version information after ADS stream restart (#5422)
xds/xdsclient: fix goroutine leaks when load reporting is enabled (#5505)
xds/ringhash: fix config update processing to recreate ring and picker when min/max ring size changes (#5557)
xds/ringhash: avoid recreating subChannels when update doesn't change address weight information (#5431)
xds/priority: fix bug which could cause priority LB to block all traffic after a config update (#5549)
xds: fix bug when environment variable GRPC_EXPERIMENTAL_ENABLE_OUTLIER_DETECTION is set to true (#5537)