Split integration test file (#42)

## Problem

Currently all of our integration tests are included in a single file,
making it hard to navigate and read.

## Solution

This PR splits the integration tests into multiple files: `common.rs`
for common helper code (eg. generate index name), and two files for
control plane and data plane integration tests.

## Type of Change

- [ ] 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

All existing test cases pass

pinecone_sdk/tests/common.rs

@@ -0,0 +1,53 @@
+use pinecone_sdk::pinecone::data::Namespace;
+use rand::Rng;
+
+/// Generates a random string of length 10
+pub fn generate_random_string() -> String {
+    use rand::distributions::Alphanumeric;
+    use rand::{thread_rng, Rng};
+
+    let s: String = thread_rng()
+        .sample_iter(&Alphanumeric)
+        .take(10)
+        .map(char::from)
+        .collect();
+
+    s.to_lowercase()
+}
+
+/// Generates a random index name
+pub fn generate_index_name() -> String {
+    format!("test-index-{}", generate_random_string())
+}
+
+/// Generates a random collection name
+pub fn generate_collection_name() -> String {
+    format!("test-collection-{}", generate_random_string())
+}
+
+/// Generates a random namespace name
+pub fn generate_namespace_name() -> Namespace {
+    let name = format!("test-namespace-{}", generate_random_string());
+    name.into()
+}
+
+/// Generates a random vector of length `length`
+pub fn generate_vector(length: usize) -> Vec<f32> {
+    let mut rng = rand::thread_rng();
+    (0..length).map(|_| rng.gen()).collect()
+}
+
+/// Returns the name of the serverless index from the environment variable
+pub fn get_serverless_index() -> String {
+    std::env::var("SERVERLESS_INDEX_NAME").unwrap()
+}
+
+/// Returns the name of the pod collection from the environment variable
+pub fn get_pod_index() -> String {
+    std::env::var("POD_INDEX_NAME").unwrap()
+}
+
+/// Returns the name of the collection from the environment variable
+pub fn get_collection() -> String {
+    std::env::var("COLLECTION_NAME").unwrap()
+}