Fix: Connection parameters apply state normalization

[AdamCoulterOz]

Summary

• normalize connection parameter state so apply never leaves unknown values behind
• preserve known configured values when the API returns a partial or redacted parameter payload
• add regression coverage for omitted and invalid connection parameter inputs

Testing

• go test ./internal/services/connection
• PATH="$(go env GOPATH)/bin:$PATH" make precommit

Checklist

• Data Transfer Objects (dtos) in dto.go
• Resource Model in model.go
• API Client functions in api_{name}.go
• Resource Implementation in resource_{name}.go
• Unit Tests in resource_{name}_test.go for Happy Path, Error conditions, boundry cases
• Acceptance Tests in resource_{name}_test.go for Happy Path
• Resource Added to provider.go and provider_test.go
• Example in the /examples folder
• Schema documented using MarkdownDescription
• Change log entry added with Changie (fixed, issue 1139)
• Run make precommit before PR

Refs #1139