(cherry picked from commit 124992d)

* Fixed device not reconnecting after MQTT connection loss

* formatting

(cherry picked from commit edb5d62)

* TLS support + fingerprint attribute in config file ( #399 )
Credit @adriancuzman

(cherry picked from commit 00843f3)
(cherry picked from commit c63aeb6)

* Refactor SSL to only compile when enabled (`#if ASYNC_TCP_SSL_ENABLED`)

(cherry picked from commit 2a8a8f1)
(cherry picked from commit 050cc8b)

* corrected string and char array length

(cherry picked from commit 107fbdf)

* documented how to use SSL encryption for MQTT

(cherry picked from commit ebac43a)

* replaced board esp01 with esp01_1m due to failing CI builds because of growing image size

When the configSize is MAX_JSON_CONFIG_FILE_SIZE the '\0' is written
after the buffers end. Don't load config files with a
size >= MAX_JSON_CONFIG_FILE_SIZE.

Signed-off-by: Philipp Rosenberger <code@iluminat23.org>

* Migrate the code from ArduinoJson v5 to v6
* Resolve memory allocation issues resulting from the migration
* Reduce unnecessary copying of some JSON related strings
* Change to StaticJsonBuffer if possible
* Use C++ casts instead of C-style casts
* Remove unnecessary comments
* Serialize JsonDocument instead of JsonObject

* Fix wrong MQTT topic buffer size calulation which might lead to a buffer overflow

…topic is truncated (#526)

* Declare _mqttTopicCopy in BootNormal.hpp
* Using _mqttTopicCopy to manage subscribed topics
* Removed leading spaces

…#641) (#642)

Removed the lines copying the sketch MD5 at the BootNormal constructor
since that crashed the firmware. At that point the ESP object is not ready
to invoke getSketchMD5(). Also the code was duplicated since it's was
already invoked at the BootNormal::setup function with no issues.

Signed-off-by: Aitor Iturrioz <riturrioz@gmail.com>

* Simplify JSON lookups
* Remove unnecessary lookups
* Add null checks for JSON strings before calling strlen()

Only copy the topic on the first message chunk. Otherwise the old copy will be
destroyed on subsequent calls to `_onMqttMessage()` for the same message, while
the copy is still being referenced by `_mqttTopicLevels`. This leads to undefined
behaviour.

…8266 into develop-v3