Linting: secure pin generation

[tibroc]

Probably not really important in our case, more for documentation purposes:

bandit throws the following warning for the pin generation in

• https://github.com/bigbluebutton/bigbluebutton-room-media-connector/blob/main/pairing-server/app.py#L25
• https://github.com/bigbluebutton/bigbluebutton-room-media-connector/blob/main/pairing-server/app.py#L127

>> Issue: [B311:blacklist] Standard pseudo-random generators are not suitable for security/cryptographic purposes.
   Severity: Low   Confidence: High
   CWE: CWE-330 (https://cwe.mitre.org/data/definitions/330.html)
   More Info: https://bandit.readthedocs.io/en/1.7.8/blacklists/blacklist_calls.html#b311-random
   Location: ./app.py:127:18