docs: write a lot of words about heartbeats (#14679)
docs: write a lot of words about heartbeats (#14679)

* docs: write a lot of words about heartbeats

Alternative to #14670

* Apply suggestions from code review

Co-authored-by: Tim Gross <e78f7fff3e6d0b12086e88217430be86de25b0e8@hashicorp.com>

* use descriptive title for link

* rework example of high failover ttl

Co-authored-by: Tim Gross <e78f7fff3e6d0b12086e88217430be86de25b0e8@hashicorp.com>
hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad,hashicorp/nomad