fix: ensure at least one of

[tenthirtyam]

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Summary of Pull Request

Includes changes to the resource_vmc.go and vmc.md files to enforce that either sddc_name or sddc_id must be provided, but not both. These changes ensure proper validation and documentation for the VMware Cloud Services resource.

Validation improvements:

• resource_vmc.go: Added ExactlyOneOf validation to enforce that either sddc_id or sddc_name must be provided. [1] [2]

Documentation updates:

• vmc.md: Updated the argument reference to reflect that sddc_name and sddc_id are required, and added a note specifying that only one of them must be provided.

Type of Pull Request

• This is a bug fix.
• This is an enhancement or feature.
• This is a code style/formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is a chore update
• This is something else.
  Please describe:

Related to Existing Issues

Issue Number: N/A

Test and Documentation Coverage

For bug fixes or features:

• Tests have been completed.
• Documentation has been added/updated.

terraform validate
╷
│ Warning: Provider development overrides are in effect
│ 
│ The following provider development overrides are set in the CLI configuration:
│  - vmware/hcx in /Users/johnsonryan/go/bin
│ 
│ The behavior may therefore not match any released version of the provider and applying changes may cause the state to become incompatible with published releases.
╵
╷
│ Error: Invalid combination of arguments
│ 
│   with hcx_vmc.example,
│   on hcx.tf line 19, in resource "hcx_vmc" "example":
│   19:   sddc_name   = "example"
│ 
│ "sddc_name": only one of `sddc_id,sddc_name` can be specified, but `sddc_id,sddc_name` were specified.
╵
╷
│ Error: Invalid combination of arguments
│ 
│   with hcx_vmc.example,
│   on hcx.tf line 20, in resource "hcx_vmc" "example":
│   20:   sddc_id   = "example"
│ 
│ "sddc_id": only one of `sddc_id,sddc_name` can be specified, but `sddc_id,sddc_name` were specified.
╵

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

[andybeltz]

LGTM