sdk-usage, modification in function names and modification in jpgs

doc/images/Invoker_discover.png

doc/images/Invoker_onboarding.png

doc/images/OpenCAPIF-icon.jpg

doc/images/invoker_get_token.png

doc/images/invoker_update-offboard.png

doc/images/provider_onboarding.png

doc/images/provider_publish.png

doc/images/provider_update-offboard.png

doc/sdk-configuration.md

doc/sdk-usage.md

scripts/provider_capif_connector_offboarding.py

scripts/provider_capif_connector_update.py

sdk/sdk.py