Add a new tailcfg.NodeCapability (NodeAttrDisableCacheNetworkMaps) to allow the
policy document to override whether a node will receive the cache-network-maps
attribute by default. The client does not interpret this attribute directly, it
is used to influence decisions by the control plane.
As of 2026-06-01, cache-network-maps is only sent when explicitly requested by
the policy. In a future version, we will send it by default for clients with a
sufficient capability version (to be added in a future commit), except to
ephemeral nodes, unless the policy sets disable-cached-network-maps.
Updates #12639
Updates tailscale/projects#28
Change-Id: I6376376d7898f7da8db977e457dcd45df9deef41
Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>