exporter is establishing connection with appname=sdk without using the connection pool

[maulal]

Describe the bug
Usually when using the parameter --mongodb.global-conn-pool the exporter establishes some permanent connections with appname=mongodb_exporter, except for the pbm collector, this one is using appname=sdk and open/close connection are made each time the exporter is scraped.

To Reproduce
Steps to reproduce the behavior:

1. what parameters are being passed to mongodb_exporter:
   mongodb_exporter --compatible-mode --discovering-mode --mongodb.global-conn-pool --log.level=info --collect-all
   MONGODB_URI=mongodb://monitor:xxx@127.0.0.1:27017/admin?serverSelectionTimeoutMS=5000
2. describe steps to reproduce the issue:
   start the exporter and scrap the metrics, you should see in the mongodb logs some sdk connections ^^ that's all

Expected behavior
We should only have connections with the same appname: mongo_exporter
We should also have only one connection during the startup of the exporter... we should not have some connection/disconnection while scraping metrics with --mongodb.global-conn-pool.

Logs
good mongodb_exporter logs:

{"t":{"$date":"2025-05-15T09:12:00.122+02:00"},"s":"I",  "c":"NETWORK",  "id":51800,   "ctx":"conn152","msg":"client metadata","attr":{"remote":"127.0.0.1:64484","client":"conn152","doc":{"application":{"name":"mongodb_exporter"},"driver":{"name":"mongo-go-driver","version":"1.17.3"},"os":{"type":"linux","architecture":"amd64"},"platform":"go1.23.7"}}}

bad mongodb_exporter logs:

{"t":{"$date":"2025-05-15T09:13:56.571+02:00"},"s":"I",  "c":"NETWORK",  "id":51800,   "ctx":"conn155","msg":"client metadata","attr":{"remote":"10.192.132.46:57340","client":"conn155","doc":{"application":{"name":"sdk"},"driver":{"name":"mongo-go-driver","version":"1.17
.3"},"os":{"type":"linux","architecture":"amd64"},"platform":"go1.23.7"}}}

Environment

• MongoDB exporter 0.44.0