New Features

client: support channel idleness using WithIdleTimeout dial option (#6263)
- This feature is currently disabled by default, but will be enabled with a 30 minute default in the future.
client: when using pickfirst, keep channel state in TRANSIENT_FAILURE until it becomes READY (gRFC A62) (#6306)
xds: Add support for Custom LB Policies (gRFC A52) (#6224)
xds: support pick_first Custom LB policy (gRFC A62) (#6314) (#6317)
client: add support for pickfirst address shuffling (gRFC A62) (#6311)
xds: Add support for String Matcher Header Matcher in RDS (#6313)
xds/outlierdetection: Add Channelz Logger to Outlier Detection LB (#6145)
- Special Thanks: @s-matyukevich
xds: enable RLS in xDS by default (#6343)
orca: add support for application_utilization field and missing range checks on several metrics setters
balancer/weightedroundrobin: add new LB policy for balancing between backends based on their load reports (gRFC A58) (#6241)
authz: add conversion of json to RBAC Audit Logging config (#6192)
authz: add support for stdout logger (#6230 and #6298)
authz: support customizable audit functionality for authorization policy (#6192 #6230 #6298 #6158 #6304 and #6225)

Bug Fixes

orca: fix a race at startup of out-of-band metric subscriptions that would cause the report interval to request 0 (#6245)
xds/xdsresource: Fix Outlier Detection Config Handling and correctly set xDS Defaults (#6361)
xds/outlierdetection: Fix Outlier Detection Config Handling by setting defaults in ParseConfig() (#6361)

orca: allow a ServerMetricsProvider to be passed to the ORCA service and ServerOption (#6223)