[ENG-4158]feat: show displayName for nested objects

[anushat05]

What does this change do?

• Read-field labels now prefer the builder's mapToDisplayName from amp.yaml over the provider's displayName.
• Nested fields have no provider metadata for their path, so the server falls back to TitleCase(fieldName) — as a result users saw $['Customer']['Email'].
• New shared getFieldDisplayName() in src/utils/manifest.ts, precedence: mapToDisplayName → displayName → mapToName → fieldName
• Used in the Configure view (RequiredFields, OptionalFieldsV2) and the InstallWizard (FieldsContent, ConfigureObjectsStep, ReviewStep).
• subPageUtils loses its local copy of getFieldDisplayName; its two consumers now import the shared helper directly.

Testing

• Added new unit tests.
• Manual E2E: deployed a Housecall Pro estimates integration, verified in the MailMonkey demo app against a local build.
  • before: $['Customer']['Email'], $['Customer']['First_name'],

• after: Customer Email, Customer First Name, customer_home_number, …

• Test integration was:

{
  "name": "hcpReadTest",
  "provider": "housecallPro",
  "displayName": "HCP Read Test",
  "read": {
    "objects": [
      {
        "objectName": "estimates",
        "destination": "test-webhook",
        "schedule": "0 * * * *",
        "mapToName": "estimate",
        "mapToDisplayName": "Estimate",
        "requiredFields": [
          {
            "fieldName": "id"
          },
          {
            "fieldName": "status"
          },
          {
            "fieldName": "$['customer']['email']",
            "mapToName": "customer_email",
            "mapToDisplayName": "Customer Email"
          },
          {
            "fieldName": "$['customer']['home_number']",
            "mapToName": "customer_home_number"
          },
          {
            "fieldName": "$['customer']['work_number']"
          },
          {
            "fieldName": "company_name",
            "mapToName": "hatch_company",
            "mapToDisplayName": "Hatch Company"
          },
          {
            "fieldName": "work_status",
            "mapToName": "hatch_work_status"
          },
          {
            "mapToName": "hatch_priority",
            "mapToDisplayName": "Priority",
            "prompt": "Which Housecall Pro field tracks priority?"
          },
          {
            "mapToName": "hatch_source",
            "prompt": "Which Housecall Pro field records the lead source?"
          }
        ],
        "optionalFields": [
          {
            "fieldName": "lead_source"
          },
          {
            "fieldName": "estimate_number",
            "mapToName": "hatch_estimate_number",
            "mapToDisplayName": "Hatch Estimate Number"
          },
          {
            "fieldName": "address",
            "mapToName": "hatch_address"
          },
          {
            "mapToName": "hatch_optional_tag",
            "mapToDisplayName": "Optional Tag",
            "prompt": "Which field holds an optional tag?"
          }
        ]
      },
      {
        "objectName": "customers",
        "destination": "test-webhook",
        "schedule": "0 * * * *",
        "requiredFields": [
          {
            "fieldName": "id"
          },
          {
            "fieldName": "email"
          }
        ],
        "optionalFields": [
          {
            "mapToName": "hatch_customer_tier",
            "mapToDisplayName": "Customer Tier",
            "prompt": "Which field records the customer tier?"
          }
        ],
        "optionalFieldsAuto": "all"
      }
    ]
  }
}```

[linear]

ENG-4158