fix: correct bandit path and activate flake8

[shawaj]

Issue

• Link: Enable flake8 #140
• Summary: enable flake8 and fix the issues it finds (51 total)

How

• fix bandit path
• activate flake8
• fix flake8 errors
• fix bandit errors
• add .github/linters/.flake8 config file with 120 character limit
• exclude generated protos with _pb2.py file ending
• change to super linter slim version, for quicker linting
• remove f string from logging.Formatter as per https://docs.python.org/3/howto/logging-cookbook.html
• change bare except to except Exception:
• correct unit test path for gatewayconfig
• add minimum unit test coverage of 70%

Screenshots

References

Relates-to: #140
Original lint logs - https://github.com/NebraLtd/hm-config/runs/4418032109?check_suite_focus=true and at logs_2850.zip

Checklist

• Tests added
• Cleaned up commit history (rebase!)
• Documentation added
• Thought about variable and method names

[shawaj]

Bandit test results:

Test results:
>> Issue: [B110:try_except_pass] Try, Except, Pass detected.
   Severity: Low   Confidence: High
   Location: ./gatewayconfig/bluetooth/characteristics/wifi_connect_characteristic.py:74:12
   More Info: https://bandit.readthedocs.io/en/latest/plugins/b110_try_except_pass.html
73	                self.connect_to_wifi(self.wifi_service, self.wifi_password)
74	            except Exception:
75	                pass
76	

--------------------------------------------------
>> Issue: [B105:hardcoded_password_string] Possible hardcoded password: 'invalid'
   Severity: Low   Confidence: Medium
   Location: ./gatewayconfig/constants.py:96:24
   More Info: https://bandit.readthedocs.io/en/latest/plugins/b105_hardcoded_password_string.html
95	WIFI_ERROR = "error"
96	WIFI_INVALID_PASSWORD = "invalid"
97	
98	# WiFi Status Mapping
99	WIFI_STATUSES = {

--------------------------------------------------

Have ignored the B105 error as this is a false positive.

For the B101 error I changed the code in question to:

        if self.wifi_service and self.wifi_password:
            try:
                self.connect_to_wifi(self.wifi_service, self.wifi_password)
            except Exception:
                logger.exception("Wifi connect failed for unknown reason")