Add has_index() (#385)

## Problem

Currently, users can not easily check if an index exists or not. The
.names() iterator on the list_indexes response object is not super
discoverable.

## Solution
Add has_index() which internally calls describe_index() and returns true
if the index exists, false otherwise.

## Type of Change

- [X] New feature (non-breaking change which adds functionality)

## Test Plan

Added integration tests.


---
- To see the specific tasks where the Asana app for GitHub is being
used, see below:
  - https://app.asana.com/0/0/1207972900637843

Author: rohanshah18

pinecone/control/pinecone.py

@@ -544,6 +544,33 @@ def describe_index(self, name: str):
 
         return IndexModel(description)
 
+    def has_index(self, name: str) -> bool:
+        """Checks if a Pinecone index exists.
+
+        :param name: The name of the index to check for existence.
+        :return: Returns `True` if the index exists, `False` otherwise.
+
+        ### Example Usage
+
+        ```python
+        import os
+        from pinecone import Pinecone
+
+        api_key = os.environ.get("PINECONE_API_KEY")
+        pc = Pinecone(api_key=api_key)
+
+        if pc.has_index("my_index_name"):
+            print("The index exists")
+        else:
+            print("The index does not exist")
+        ```
+        """
+
+        if name in self.list_indexes().names():
+            return True
+        else:
+            return False
+
     def configure_index(
         self,
         name: str,
@@ -737,12 +764,12 @@ def Index(self, name: str = "", host: str = "", **kwargs):
 
         pc = Pinecone(api_key=api_key)
         pc.create_index(
-            name='my-index',
+            name='my_index',
             dimension=1536,
             metric='cosine',
             spec=ServerlessSpec(cloud='aws', region='us-west-2')
         )
-        index = pc.Index('my-index')
+        index = pc.Index('my_index')
 
         # Now you're ready to perform data operations
         index.query(vector=[...], top_k=10)

tests/integration/control/serverless/test_has_index.py

@@ -0,0 +1,18 @@
+from tests.integration.helpers import random_string
+
+
+class TestHasIndex:
+    def test_index_exists_success(self, client, create_sl_index_params):
+        name = create_sl_index_params["name"]
+        client.create_index(**create_sl_index_params)
+        has_index = client.has_index(name)
+        assert has_index == True
+
+    def test_index_does_not_exist(self, client):
+        name = random_string(8)
+        has_index = client.has_index(name)
+        assert has_index == False
+
+    def test_has_index_with_null_index_name(self, client):
+        has_index = client.has_index("")
+        assert has_index == False