feat: support for client cert and multiple host connection string for mongo adapter

[aneojgurhem]

Support for multiple client certificates. Clients we use supports it. May be used for certificate rotation.

Environment variable to set up client certificates:

MongoDB__ClientCertificateFiles__0=/path/to/pem/file0
MongoDB__ClientCertificateFiles__1=/path/to/pem/file1

Beware that client certificate files should be mounted in the container at the location given by the environment variables.

Support for multiple hosts has been added. The follonwing code shows how to specify multiple hosts:

MongoDB__Hosts__0=mongo0:27017
MongoDB__Hosts__1=mongo1:27017

Beware that MongoDB__Host and MongoDB__Port were removed in this PR.

MongoDB__Host=mongo
MongoDB__Port=27017

is now equivalent to

MongoDB__Hosts__0=mongo:27017

Finally, a variable to change mongo connection scheme has been introduced. It takes two values:

MongoDB__Scheme=MongoDB
MongoDB__Scheme=MongoDBPlusSrv