[Salesforce Connector] Check if given object type exists before attempting to fetch it

[jedrazb]

Bug Description

Currently Salesforce connector makes certain assumptions about standard objects present in the Salesforce schema, if .e.g account object type is not present, connector will simply fail the sync with NOT_FOUND error.

To Reproduce

Steps to reproduce the behavior:

1. Use salesforce instance with limited standard objects (.e.g exclude contacts)
2. Try syncing
3. Observe NOT_FOUND error

Expected behavior

We should be more robust when object types are missing, and ideally

• skip fetching objects if they don't exist/aren't accessible in a given instance
• log warning that specific objects were skipped
• log error if no data/objects were accessible to be fetched