docs(get-started): add information about the Agent and JMX config (#104)

* docs(get-started): add information about the Agent and JMX config

* typo

* rephrase

* quotes and typo

* add anchors

* openshift -> kubernetes

* add note about maven registry auth

* add comments

* accept suggestion

* typo

* formatting

* typo

* formatting

* break comment lines

* use yaml multiline

* plural

* rephrase

* add explanation comment

* fixup! add explanation comment

* rebase fix

* list configuration combinations before explaining them

* add links

* rephrase

* fix typo

* fixup! fix typo

* explain agent deployment environment variables more

* explain cross-namespace Agent and Cryostat

* reference agent version 0.2.1

* in hybrid agent setup, skip the jfr-jmx named port

* set explicit hostname for JMX

* reorganize