revert to an earlier lib version to support TLS

[MiaAltieri]

New TLS lib breaks TLS in MongoDB charm:

• the mongoDB replicas are not able to communicate with each other and the units
• leader consistently becomes unhealhty and un reachable

unit-mongodb-k8s-1: 15:36:42 INFO unit.mongodb-k8s/1.juju-log {"message": "Waiting for suitable server to become available", "selector": "Primary()", "operation": "replSetGetStatus", "topologyDescription": "<TopologyDescription id: 6644d68ab6d8f3de582cd1e7, topology_type: ReplicaSetNoPrimary, servers: [<ServerDescription ('mongodb-k8s-0.mongodb-k8s-endpoints', 27017) server_type: Unknown, rtt: None>, <ServerDescription ('mongodb-k8s-1.mongodb-k8s-endpoints', 27017) server_type: Unknown, rtt: None>, <ServerDescription ('mongodb-k8s-2.mongodb-k8s-endpoints', 27017) server_type: Unknown, rtt: None>]>", "clientId": {"$oid": "6644d68ab6d8f3de582cd1e7"}, "remainingTimeMS": 0}

[juditnovak]

Re-reviewing after unittests are fixed. (As I assume this is what you would need, no...?)

[juditnovak]

LGTM