Feature Request: Support Boto3 Client When Using BedrockEncoder

[drobbins-ancile]

Currently when instantiating a BedrockEncoder we are required to set the access key id, secret key, and session token. This is awkward and not ideal for long-running services like API's as the session credentials expire.

I am requesting that the BedrockEncoder support providing a boto3 client that is created outside of the encoder. This will support automatically refreshing the credentials and match the behavior of other frameworks that use the bedrock API.

It appears that there is already a client parameter available when creating a BedrockEncoder but it isn't used.

Perhaps we could support something like the following?

import boto3
from semantic_router.encoders import BedrockEncoder

boto3_client = boto3.client("bedrock-runtime")

encoder = BedrockEncoder(
	name="amazon.titan-embed-text-v2:0",
	client=boto3_client
)

The existing logic in the encoder would be modified to only create a new client if one is not provided:

import boto3
from semantic_router.encoders import BaseEncoder

class BedrockEncoder(BaseEncoder):
    client: boto3.client = None
	...


if not self.client:
      self.access_key_id = self.get_env_variable("AWS_ACCESS_KEY_ID", access_key_id)
      self.secret_access_key = self.get_env_variable(
          "AWS_SECRET_ACCESS_KEY", secret_access_key
      )
      self.session_token = self.get_env_variable("AWS_SESSION_TOKEN", session_token)
      self.region = self.get_env_variable(
          "AWS_DEFAULT_REGION", region, default="us-west-1"
      )
      self.input_type = input_type
      try:
          self.client = self._initialize_client(
              self.access_key_id,
              self.secret_access_key,
              self.session_token,
              self.region,
          )
      except Exception as e:
          raise ValueError(f"Bedrock client failed to initialise. Error: {e}") from e

The access_key_id, secret_access_key, and region parameters are already optional.