In Nomad 1.6.0 we started sending the node secret with RPCs that previously did
not include it. We planned to deprecate the older auth workflow but didn't set a
release. Removing the legacy support means that nodes running <1.6.0 will fail
to heartbeat.
Ref: https://hashicorp.atlassian.net/browse/NET-10009
Add a section to the docs describing planned upcoming deprecations and
removals. Also added some missing upgrade guide sections missed during the last
release.
We no longer intend to release 32-bit builds for any platform. We'd previously
removed the builds for i386 on both Linux and Windows, but never got around to
removing the ARM builds. Add a note about this deprecation in the release notes
for 1.8.x.
