INTMDB-158: Added private endpoint in connection strings

[coderGo93]

Description

• Added private_endpoint for schema connection_strings in resource and datasource(s) of cluster
• Updated docs for resource and datasource(s) of cluster
• Modified test using the new private endpoint instead of deprecated ones

Link to any related issue(s):

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
• Documentation fix/enhancement

Required Checklist:

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

Further comments

Tests will fail until it can be updated with recent version of client mongodb because of a bug related to object of PrivateEndpoint

[themantissa]

LGTM - once the go client is updated the test should pass. Just need DoU review. Thanks!

[leofigy]

Looks good :)