roachtest: jepsen run an ntp server on controller node to enable clock skew tests

[aliher1911]

Currently clock skew tests are disabled:

cockroach/pkg/cmd/roachtest/tests/jepsen.go

Lines 38 to 42 in 21a286f

	// TODO(bdarnell): subcritical-skews nemesis is currently flaky due to ntp rate limiting.
	// https://github.com/cockroachdb/cockroach/issues/35599
	//{"subcritical-skews", "--nemesis subcritical-skews"},
	//{"majority-ring-subcritical-skews", "--nemesis majority-ring --nemesis2 subcritical-skews"},
	//{"subcritical-skews-start-kill-2", "--nemesis subcritical-skews --nemesis2 start-kill-2"},

Because of #35599.

Tests rely directly on ntp.ubuntu.com which starts throttling requests pretty quickly making tests flaky.

It should be easy to install an ntp package to the controller node only and point tests to use it since we could pass its IP to the test from roachtest. We need to check how it would interact with chrony or to disable chrony on controller.

Jira issue: CRDB-12064

[aliher1911]

This could be done pretty easily by passing ntp server to test and then adding 'allow' to chronyd configuration on controller. No need to run ntpd as chronyd has ntpd functionality that is not enabled by default.
But easier solution could be to just use pool.ntp.org instead. We should try that first and only proceed with this approach if using pool still fails. (see #35599)

[aliher1911]

This is resolved as we now use ntp that doesn't throttle us.