`mongo_exporter` fails to authorize when MongoDB running with `authMechanism=MONGODB-X509`

pmm-admin version: 2.13.0

mongo version: 4.4 - Percona

mongo_exporter is able to connect to mongo with --tls, --tls-certificate-key-file and --tls-ca-file, but then gets errors on Mongo side because of missing authorization.

"error getting cluster ID: (Unauthorized)"

Straight connection to mongo shell works with same flags when following mongo flags are added:

--authenticationDatabase '$external' --authenticationMechanism MONGODB-X509

I do not see that pmm supports these flags.

How to test:

This repo contains files to generate and test mongo with auth x509 https://github.com/askomorokhov/mongo-x509-auth-ssl

1. clone repo https://github.com/askomorokhov/mongo-x509-auth-ssl
2. gen certificate ./generate-certs mongo-x509
3. build container docker build -t my-mongo-x509 --no-cache .
4. run pmm docker-compose up -d pmm-client-bin mongo-x509
5. Copy certificates: https://github.com/askomorokhov/mongo-x509-auth-ssl/blob/master/docker-compose.yaml#L41-L50

   1. docker cp mongo-x509:/etc/ssl/mongodb-CA.pem mongodb-CA.pem
      docker cp mongo-x509:/etc/ssl/mongodb-client.pem mongodb-client.pem
      docker cp mongodb-client.pem pmm-client:/etc/ssl/mongodb-client.pem
      docker cp mongodb-CA.pem pmm-client:/etc/ssl/mongodb-CA.pem
       
       

6. go into pmm-client container: docker exec -ti pmm-client bash
7. login into mongo:
   mongo mongo-x509:27017/admin --ssl --sslPEMKeyFile /etc/ssl/mongodb-client.pem --sslCAFile /etc/ssl/mongodb-CA.pem --authenticationDatabase '$external' --authenticationMechanism MONGODB-X509 --username "C=US,ST=CA,L=San Francisco,O=Jaspersoft,OU=JSDev,CN=admin"
    
8. 
   configure mongo https://www.percona.com/doc/percona-monitoring-and-management/2.x/setting-up/client/mongodb.html

9.  run some load

10. start mongo monitoring:
    pmm-admin add mongodb --tls --tls-certificate-key-file=/etc/ssl/mongodb-client.pem --tls-ca-file=/etc/ssl/mongodb-CA.pem --authentication-mechanism='MONGODB-X509' --authentication-database='$external' --host=mongo-x509 MyMongoX509