CLOUDP-167925: add support for PrivateEndpoint.srvShardOptimizedConnectionString

[tibulca]

Description

CLOUDP-167925: add support for PrivateEndpoint.srvShardOptimizedConnectionString
https://www.mongodb.com/docs/atlas/reference/api-resources-spec/#tag/Multi-Cloud-Clusters/operation/getCluster (see response samples connectionStrings.privateEndpoint)

Type of change:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Required Checklist:

• I have signed the MongoDB CLA
• I have added tests that prove my fix is effective or that my feature works
• I have added any necessary documentation (if appropriate)
• I have run make fmt and formatted my code

Further comments