add filer configuration options for username/password and tls

[baursn]

What problem are we solving?

a secure mongodb setup with security comes with tls/ssl encryption and user authentication. The filer mongodb backend did only support connecting without encryption and authentication. This PR adds support for that.

How are we solving the problem?

Configuration in filer.toml can now be extended with additional configuration parameters as in this example:

[mongodb]
enabled = true
uri = "mongodb://localhost:27017/tls=true"
username = "seaweedfs"
password = "seaweedfs"
database = "seaweedfs"
ssl = true
ssl_ca_file = "./mongodb/ssl/ca.crt"
ssl_cert_file = "./mongodb/ssl/client.pem"
ssl_key_file = "./mongodb/ssl/client.pem"

How is the PR tested?

Tested with my mongodb setup.

Checks

• I have added unit tests if possible.
• I will add related wiki document changes and link to this PR after merging.
  i think there is no dedicated wiki page for monodb yet, but if needed i can update wiki

[chrislusf]

please add an option insecure_skip_verify similar to https://github.com/seaweedfs/seaweedfs/blob/master/weed/filer/arangodb/arangodb_store.go#L64

[chrislusf]

@baursn ^^

[baursn]

good catch, added in #5602