* Refactor component heartbeat callbacks
Consolidate the OK/degraded broadcasts so the same logic isn't
duplicated for each component.
* Periodically update discovered desktops
Fixes#8644
* Allow customizing the desktop search
With this change, we support a discovery base DN other than '*',
and add support for further filtering the results with additional
LDAP filters.
Additionally, we filter out group managed service accounts, which
show up in LDAP searches for (objectClass=computer), despite not
being comptuers. (This is mostly harmless, as the service accounts
aren't present in DNS, so Teleport just ignores them. It does, however,
log a DNS error message that could be confusing, so we explicitly
filter these out just to be safe. This was discovered when testing
on AWS managed AD, which creates a gMSA for DNS.
Zac Bergquist
ce03d2cdea