Configuration flag to bypass duplicate message filtering on mapper startup

[albinsuresh]

Is your feature improvement request related to a problem? Please describe.

The mapper currently avoids sending duplicate entity registration messages to the cloud on startup, by ignoring the resent registration messages for the entities that are already present in the restored persistent entity store. But, if someone intentionally/accidentally wipes the entities from the cloud, they will never be recreated again by the mapper, due to this filtering mechanism. So, a mechanism to disable this filtering on startup is desired to ease the syncing of the entire entity state on tedge to the cloud.

Describe the solution you'd like

Introduce a c8y.entity_store.sync_on_startup boolean config flag to enable the above mentioned forced syncing on startup. The default value should be false, to keep the current filtering mechanism as the default.

[didier-wenzek]

A new tedge config settings has been added: c8y.entity_store.clean_start.
This control the messages sent to Cumulocity IoT on mapper restart.

• The default setting is for c8y.entity_store.clean_start to be false. Only new services and child-devices, created while the c8y mapper was down, are published to the Cumulocity IoT on mapper restart.
• When c8y.entity_store.clean_start is set to false, the whole state of the device, services and child-devices is resent to the cloud.

[gligorisaev]

QA has thoroughly checked the feature and here are the results:

• Test for ticket exists in the test suite.
• QA has tested the function and it's functioning according description.