cleanup

This PR fix two bugs in current version :
- #1189 
- #1182

Adds docs on 
- discovering what other nodes are connected to a given node type
- discovering what node properties are present on a given node type

Updates docs on
- roadmap link
- making syncmetadata docs more discoverable

…iple intel modules (#1214)

See #1210 for full context.

#1154 tried to solve this problem by updating the querybuilder but this
was too complex and would not generalize well.

This solution is simpler where we use different property classes for
each API response so that we don't overwrite properties on a node set by
another sync job.

This PR can be reviewed commit-by-commit:
- c0d9ac4 shows a repro of the error
with a failing integration test.
- facb63b shows the solution using
multiple classes.

---------

Co-authored-by: Ramon Petgrave <[email protected]>

It's possible for neo4j sessions `read_transaction` in `get_state` to
return an empty list in the drift detection module.

This PR ensures that there are entries before referencing index 0.
```
File "/code/venvs/venv/lib/python3.8/site-packages/cartography/driftdetect/get_states.py", line 123, in get_query_state
    get_state(session, state)
  File "/code/venvs/venv/lib/python3.8/site-packages/cartography/driftdetect/get_states.py", line 148, in get_state
    state.properties = list(new_results[0].keys())
IndexError: list index out of range
```

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