Added default "measurement" state_class

[derolli1976]

Allow long term statistics.

Description

Added default "measurement" state_class to all numeric sensors.

Motivation and Context

Sensors missing "measurement" state_class do not show up in HA long term statistics

Screenshots (if appropriate):

Types of changes

• [x ] 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 change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.