Closes gh-8842

* pr/8683:
  Polish "Add support for HotSwapAgent to devtools"
  Add support for HotSwapAgent to devtools

Closes gh-8683

HotSwapAgent is an open source competition to JRebel. This commit adds
"org.hotswap.agent.HotswapAgent" to the list of known Java agent based
class reloaders. This causes same behavior as when JRebel is used: a full
restart is NOT triggered when any class changes, however LiveReload event
is still triggered.

See gh-8683

* pr/8703:
  Polish "Document HTTP response format of health endpoint"
  Document HTTP response format of health endpoint

Closes gh-8703

Add HTTP response format details for health endpoint, including default
status codes and sample responses.

See gh-8703

This commit changes the solr health indicator to request the status of
all available cores, rather than invoking a generic ping on the admin
handler.

Recent versions of Solr now have a ping handler per core and the general
admin handler is gone, leading to incorrect health status. For backward
compatible reason the `solrStatus` attribute is kept to `OK` if all cores
are running properly (that's actually `0` behind the scenes).

Closes gh-8463

Closes gh-8876

* pr/8829:
  Allow to disable max http post size limit

Closes gh-8508

See spring-projects/spring-framework@ea5cb26d750f

* pr/8866:
  Upgrade to Spring Kafka 1.1.4

Closes gh-8866

It should have been removed in 2522a5f9

Closes gh-8702

See gh-8853 and cb34189c

Closes gh-8860

Closes gh-8859

Closes gh-8858