Behavior Changes

client: use proper "@" semantics for connecting to abstract unix sockets. (#5678)
- This is technically a bug fix; the result is that the address was including a trailing NULL byte, which it should not have. This may break users creating the socket in Go by prefixing a NULL instead of an "@", though, so calling it out as a behavior change.
- Special Thanks: @jachor

New Features

metadata: add experimental ValueFromIncomingContext to more efficiently retrieve a single value (#5596)
- Special Thanks: @horpto
stats: provide peer information in HandleConn context (#5589)
- Special Thanks: @feihu-stripe
xds: add support for Outlier Detection, enabled by default (#5435, #5673)

client: fix deadlock in transport caused by GOAWAY racing with stream creation (#5652)
- This should only occur with an HTTP/2 server that does not follow best practices of an advisory GOAWAY (not a grpc-go server).
xds/xdsclient: fix a bug which was causing routes with cluster_specifier_plugin set to be NACKed when GRPC_EXPERIMENTAL_XDS_RLS_LB was off (#5670)
xds/xdsclient: NACK cluster resource if config_source_specifier in lrs_server is not self (#5613)
xds/ringhash: fix a bug which sometimes prevents the LB policy from retrying connection attempts (#5601)
xds/ringhash: do nothing when asked to exit IDLE instead of falling back on the default channel behavior of connecting to all addresses (#5614)
xds/rls: fix a bug which was causing the channel to be stuck in IDLE (#5656)
alts: fix a bug which was setting WaitForReady on handshaker service RPCs, thereby delaying fallback when required (#5620)
gcp/observability: fix End() to cleanup global state correctly (#5623)