fix(backend): Fix 4 (deprecation) warnings on startup (#10759)

Fixes these warnings on startup:
```
/home/reinier/code/agpt/AutoGPT/autogpt_platform/backend/.venv/lib/python3.11/site-packages/pydantic/_internal/_config.py:373: UserWarning: Valid config keys have changed in V2:
* 'schema_extra' has been renamed to 'json_schema_extra'
  warnings.warn(message, UserWarning)
/home/reinier/code/agpt/AutoGPT/autogpt_platform/backend/.venv/lib/python3.11/site-packages/pydantic/_internal/_config.py:323: PydanticDeprecatedSince20: Support for class-based `config` is deprecated, use ConfigDict instead. Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.11/migration/
  warnings.warn(DEPRECATION_MESSAGE, DeprecationWarning)
/home/reinier/code/agpt/AutoGPT/autogpt_platform/backend/.venv/lib/python3.11/site-packages/pydantic/_internal/_generate_schema.py:298: PydanticDeprecatedSince20: `json_encoders` is deprecated. See https://docs.pydantic.dev/2.11/concepts/serialization/#custom-serializers for alternatives. Deprecated in Pydantic V2.0 to be removed in V3.0. See Pydantic V2 Migration Guide at https://errors.pydantic.dev/2.11/migration/
  warnings.warn(
/home/reinier/code/agpt/AutoGPT/autogpt_platform/backend/.venv/lib/python3.11/site-packages/pydantic/_internal/_fields.py:294: UserWarning: `alias` specification on field "created_at" must be set on outermost annotation to take effect.
  warnings.warn(
/home/reinier/code/agpt/AutoGPT/autogpt_platform/backend/.venv/lib/python3.11/site-packages/pydantic/_internal/_fields.py:294: UserWarning: `alias` specification on field "updated_at" must be set on outermost annotation to take effect.
  warnings.warn(
```

- Resolves #10758

### Changes 🏗️

- Fix field annotations in `backend/blocks/exa/websets.py`
- Replace deprecated JSON encoder specification in
`backend/blocks/wordpress/_api.py` by field serializer
- Move deprecated `schema_extra` example specification in
`backend/server/integrations/models.py` to `Field(examples=...)`

The two remaining warnings that appear on start-up aren't trivial to
fix.

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] Changes are trivial and do not require further testing

autogpt_platform/backend/backend/blocks/exa/websets.py

@@ -93,11 +93,11 @@ class Webset(BaseModel):
     """
     Set of key-value pairs you want to associate with this object.
     """
-    created_at: Annotated[datetime, Field(alias="createdAt")] | None = None
+    created_at: Annotated[datetime | None, Field(alias="createdAt")] = None
     """
     The date and time the webset was created
     """
-    updated_at: Annotated[datetime, Field(alias="updatedAt")] | None = None
+    updated_at: Annotated[datetime | None, Field(alias="updatedAt")] = None
     """
     The date and time the webset was last updated
     """

autogpt_platform/backend/backend/blocks/wordpress/_api.py

@@ -4,6 +4,8 @@ from logging import getLogger
 from typing import Any, Dict, List, Union
 from urllib.parse import urlencode
 
+from pydantic import field_serializer
+
 from backend.sdk import BaseModel, Credentials, Requests
 
 logger = getLogger(__name__)
@@ -382,8 +384,9 @@ class CreatePostRequest(BaseModel):
     # Advanced
     metadata: List[Dict[str, Any]] | None = None
 
-    class Config:
-        json_encoders = {datetime: lambda v: v.isoformat()}
+    @field_serializer("date")
+    def serialize_date(self, value: datetime | None) -> str | None:
+        return value.isoformat() if value else None
 
 
 class PostAuthor(BaseModel):

autogpt_platform/backend/backend/server/integrations/models.py

@@ -58,17 +58,13 @@ class ProviderConstants(BaseModel):
         default_factory=lambda: {
             name.upper().replace("-", "_"): name for name in get_all_provider_names()
         },
-    )
-
-    class Config:
-        schema_extra = {
-            "example": {
-                "PROVIDER_NAMES": {
-                    "OPENAI": "openai",
-                    "ANTHROPIC": "anthropic",
-                    "EXA": "exa",
-                    "GEM": "gem",
-                    "EXAMPLE_SERVICE": "example-service",
-                }
+        examples=[
+            {
+                "OPENAI": "openai",
+                "ANTHROPIC": "anthropic",
+                "EXA": "exa",
+                "GEM": "gem",
+                "EXAMPLE_SERVICE": "example-service",
             }
-        }
+        ],
+    )

autogpt_platform/frontend/src/app/api/openapi.json

@@ -6319,7 +6319,16 @@
             "additionalProperties": { "type": "string" },
             "type": "object",
             "title": "Provider Names",
-            "description": "All available provider names as a constant mapping"
+            "description": "All available provider names as a constant mapping",
+            "examples": [
+              {
+                "ANTHROPIC": "anthropic",
+                "EXA": "exa",
+                "EXAMPLE_SERVICE": "example-service",
+                "GEM": "gem",
+                "OPENAI": "openai"
+              }
+            ]
           }
         },
         "type": "object",