[WIP] KE compatibility (#457)

## Problem

While cleaning up and simplifying the Configuration class (which
originated from generated code but is now something we maintain by hand
for greater control), a congif attribute in use by the assistants plugin
was accidentally removed.

## Solution

Restore config attributes being used by assistants

## Type of Change

- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected)
- [ ] This change requires a documentation update
- [ ] Infrastructure change (CI configs, etc)
- [ ] Non-code change (docs, etc)
- [ ] None of the above: (explain here)

## Test Plan

Describe specific steps for validating this change.

Author: jhamon

pinecone/openapi_support/configuration.py

@@ -61,6 +61,11 @@ class Configuration:
           disabled. This can be useful to troubleshoot data validation problem, such as
           when the OpenAPI document validation rules do not match the actual API data
           received by the server.
+        :param server_operation_index: Mapping from operation ID to an index to server
+          configuration.
+        :param server_operation_variables: Mapping from operation ID to a mapping with
+          string values to replace variables in templated server configuration.
+          The validation of enums is performed for variables with defined enum values before.
         :param ssl_ca_cert: str - the path to a file of concatenated CA certificates
           in PEM format
 
@@ -95,13 +100,22 @@ def __init__(
         api_key_prefix=None,
         discard_unknown_keys=False,
         disabled_client_side_validations="",
+        server_index=None,
+        server_variables=None,
+        server_operation_index=None,
+        server_operation_variables=None,
         ssl_ca_cert=None,
     ):
         """Constructor"""
         self._base_path = "https://api.pinecone.io" if host is None else host
         """Default Base url
         """
-
+        self.server_index = 0 if server_index is None and host is None else server_index
+        self.server_operation_index = server_operation_index or {}
+        """Default server index
+        """
+        self.server_variables = server_variables or {}
+        self.server_operation_variables = server_operation_variables or {}
         """Default server variables
         """
         self.temp_folder_path = None
@@ -353,10 +367,56 @@ def auth_settings(self):
             }
         return auth
 
+    def get_host_settings(self):
+        """Gets an array of host settings
+
+        :return: An array of host settings
+        """
+        return [{"url": "https://api.pinecone.io", "description": "Production API endpoints"}]
+
+    def get_host_from_settings(self, index, variables=None, servers=None):
+        """Gets host URL based on the index and variables
+        :param index: array index of the host settings
+        :param variables: hash of variable and the corresponding value
+        :param servers: an array of host settings or None
+        :return: URL based on host settings
+        """
+        if index is None:
+            return self._base_path
+
+        variables = {} if variables is None else variables
+        servers = self.get_host_settings() if servers is None else servers
+
+        try:
+            server = servers[index]
+        except IndexError:
+            raise ValueError(
+                "Invalid index {0} when selecting the host settings. Must be less than {1}".format(
+                    index, len(servers)
+                )
+            )
+
+        url = server["url"]
+
+        # go through variables and replace placeholders
+        for variable_name, variable in server.get("variables", {}).items():
+            used_value = variables.get(variable_name, variable["default_value"])
+
+            if "enum_values" in variable and used_value not in variable["enum_values"]:
+                raise ValueError(
+                    "The variable `{0}` in the host URL has invalid value {1}. Must be {2}.".format(
+                        variable_name, variables[variable_name], variable["enum_values"]
+                    )
+                )
+
+            url = url.replace("{" + variable_name + "}", used_value)
+
+        return url
+
     @property
     def host(self):
         """Return generated host."""
-        return self._base_path
+        return self.get_host_from_settings(self.server_index, variables=self.server_variables)
 
     @host.setter
     def host(self, value):
@@ -372,6 +432,10 @@ def __repr__(self):
             f"connection_pool_maxsize={self.connection_pool_maxsize}",
             f"discard_unknown_keys={self.discard_unknown_keys}",
             f"disabled_client_side_validations={self.disabled_client_side_validations}",
+            f"server_index={self.server_index}",
+            f"server_variables={self.server_variables}",
+            f"server_operation_index={self.server_operation_index}",
+            f"server_operation_variables={self.server_operation_variables}",
             f"ssl_ca_cert={self.ssl_ca_cert}",
         ]
         return f"Configuration({', '.join(attrs)})"