Add ExposeSensor cooldown option

[farmio]

Description

• ExposeSensor: Add cooldown option to allow rate-limiting of sent telegrams.
• Add task.done() to TaskRegistry tasks.

See #765

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• The documentation has been adjusted accordingly
• Tests have been added that prove the fix is effective or that the feature works
• The changes are documented in the changelog (docs/changelog.md)

[codecov]

Codecov Report

Merging #1094 (aa819e0) into main (5121ae4) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1094      +/-   ##
==========================================
+ Coverage   96.30%   96.31%   +0.01%     
==========================================
  Files         138      138              
  Lines        8626     8654      +28     
==========================================
+ Hits         8307     8335      +28     
  Misses        319      319              

Impacted Files	Coverage Δ
xknx/core/task_registry.py	100.00% <100.00%> (ø)
xknx/devices/expose_sensor.py	100.00% <100.00%> (ø)

[farmio]

Current implementation cancels the sending of a new value with GVWrite if it was sent via GVResponse while waiting for cooldown.

Not 100% sure if this can cause troubles - probably depends on the receivers flags Settings.