MQTT: Support for certificate bundle; Client clean-up

* Closes #7040
* Merges #7041
* Update submodule: git log --oneline 9fdf7b61385633075d5c3b84803f2dd0578d7869..f10321a53b53a146ee299cfecc320b89c0cf6611

Detailed description of the changes:
* Remove unnecessary parentheses
  - esp-mqtt commit: espressif/esp-mqtt@db13533
  - esp-mqtt MR: espressif/esp-mqtt!101
* outbox: Cleanup all items when connection closes
  - esp-mqtt commit: espressif/esp-mqtt@1a94efe
  - esp-mqtt MR: espressif/esp-mqtt!104
* Outbox: Removes unnecessary calls to outbox_set_pending
  - esp-mqtt commit: espressif/esp-mqtt@36a3990
  - esp-mqtt MR: espressif/esp-mqtt!105
* MQTT: Makes abort connection function void.
  - esp-mqtt commit: espressif/esp-mqtt@67553ab
  - esp-mqtt MR: espressif/esp-mqtt!106
* Client: Removes unused defines
  - esp-mqtt commit: espressif/esp-mqtt@eec6f0e
  - esp-mqtt MR: espressif/esp-mqtt!100
  - Closes espressif/esp-mqtt#194
* Config: Added support for certificate bundle
  - esp-mqtt commit: espressif/esp-mqtt@06157be
  - esp-mqtt MR: espressif/esp-mqtt!98
  - Closes espressif/esp-mqtt#190
* Config: Adds missing field at config struct (path field)
  - esp-mqtt commit: espressif/esp-mqtt@5b27d18
  - esp-mqtt MR: espressif/esp-mqtt!96
* Client: Add support for partial transport writes
  - esp-mqtt commit: espressif/esp-mqtt@d8c9c7a
  - esp-mqtt MR: espressif/esp-mqtt!99
  - Partially addresses #6940
* Client: Add support for Retain flag in messages posted by events
  - esp-mqtt commit: espressif/esp-mqtt@a00a313
  - esp-mqtt MR: espressif/esp-mqtt!99
  - Closes espressif/esp-mqtt#193
* esp-mqtt: Added nullchecks for public APIs
  - esp-mqtt commit: espressif/esp-mqtt@2f57985
  - esp-mqtt MR: espressif/esp-mqtt!94
  - Closes espressif/esp-mqtt#185
* esp-mqtt: Reduce the includes used in all files
  - esp-mqtt commit: espressif/esp-mqtt@87fcce7
  - esp-mqtt MR: espressif/esp-mqtt!93
* mqtt_outbox: Use STAILQ_FOREACH for outbox_delete_single_expired
  - esp-mqtt commit: espressif/esp-mqtt@ff8e648
  - esp-mqtt MR: espressif/esp-mqtt!97
  - Merges espressif/esp-mqtt#187
* Client: Add optimize for depend on ssl
  - esp-mqtt commit: espressif/esp-mqtt@8f3cac8
  - esp-mqtt MR: espressif/esp-mqtt!95