Add documentation.

Author: ewbankkit

website/docs/r/bedrockagent_knowledge_base.html.markdown

@@ -184,6 +184,7 @@ The `pinecone_configuration` configuration block supports the following argument
 * `credentials_secret_arn` - (Required) ARN of the secret that you created in AWS Secrets Manager that is linked to your Amazon RDS database.
 * `database_name` - (Required) Name of your Amazon RDS database.
 * `field_mapping` - (Required) Names of the fields to which to map information about the vector store. This block supports the following arguments:
+    * `custom_metadata_field` - (Optional) Name for the universal metadata field where Amazon Bedrock will store any custom metadata from your data source.
     * `metadata_field` - (Required) Name of the field in which Amazon Bedrock stores metadata about the vector store.
     * `primary_key_field` - (Required) Name of the field in which Amazon Bedrock stores the ID for each entry.
     * `text_field` - (Required) Name of the field in which Amazon Bedrock stores the raw text from your data. The text is split according to the chunking strategy you choose.