Fix temperature checks without setpoints

Fixes error logs (non critical) that may occur when temperatures are received from the printer without setpoints.

Specifically these types of Error logs:

2024-10-18 17:40:47,936 - octoprint.plugins.preheathelper - ERROR - TraceBack: Traceback (most recent call last):
  File "/octoprint/plugins/custom/OctoPrint-PreheatHelper/octoprint_preheathelper/__init__.py", line 189, in on_temperatures_received
    if bed_target >= MINIMAL_SETPOINT_TEMPERATURE:
TypeError: '>=' not supported between instances of 'NoneType' and 'int'

2024-10-18 17:40:49,448 - octoprint.plugins.preheathelper - ERROR - TraceBack: Traceback (most recent call last):
  File "/octoprint/plugins/custom/OctoPrint-PreheatHelper/octoprint_preheathelper/__init__.py", line 194, in on_temperatures_received
    if tool_target >= MINIMAL_SETPOINT_TEMPERATURE:
TypeError: '>=' not supported between instances of 'NoneType' and 'int'

Add release channels to plugin

This is a mostly non-functional change, but introduces release channels to this plugin.

This allows me to work on new (requested) features and publish them in those new channels without affecting the stable main branch.

Minor stability improvements

Bump

Initial plugin release

V0.1.0 of the Preheat Helper plugin