premai[patch]:Standardized model init args (#21308)

[Standardized model init args
#20085](https://github.com/langchain-ai/langchain/issues/20085)
- Enable premai chat model to be initialized with `model_name` as an
alias for `model`, `api_key` as an alias for `premai_api_key`.
- Add initialization test `test_premai_initialization`

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/community/langchain_community/chat_models/premai.py

@@ -34,7 +34,13 @@ from langchain_core.messages import (
     SystemMessageChunk,
 )
 from langchain_core.outputs import ChatGeneration, ChatGenerationChunk, ChatResult
-from langchain_core.pydantic_v1 import BaseModel, Extra, SecretStr, root_validator
+from langchain_core.pydantic_v1 import (
+    BaseModel,
+    Extra,
+    Field,
+    SecretStr,
+    root_validator,
+)
 from langchain_core.utils import get_from_dict_or_env
 
 if TYPE_CHECKING:
@@ -170,10 +176,10 @@ class ChatPremAI(BaseChatModel, BaseModel):
     project_id: int
     """The project ID in which the experiments or deployments are carried out. 
     You can find all your projects here: https://app.premai.io/projects/"""
-    premai_api_key: Optional[SecretStr] = None
+    premai_api_key: Optional[SecretStr] = Field(default=None, alias="api_key")
     """Prem AI API Key. Get it here: https://app.premai.io/api_keys/"""
 
-    model: Optional[str] = None
+    model: Optional[str] = Field(default=None, alias="model_name")
     """Name of the model. This is an optional parameter. 
     The default model is the one deployed from Prem's LaunchPad: https://app.premai.io/projects/8/launchpad
     If model name is other than default model then it will override the calls 
@@ -233,6 +239,8 @@ class ChatPremAI(BaseChatModel, BaseModel):
         """Configuration for this pydantic object."""
 
         extra = Extra.forbid
+        allow_population_by_field_name = True
+        arbitrary_types_allowed = True
 
     @root_validator()
     def validate_environments(cls, values: Dict) -> Dict: