Add support for disabling TLS (#150)

## Problem

Add support for enabling/disabling TLS.

## Solution

Added enableTls boolean flag which is set to true by default but when
set to false, it will be disabled.

## Type of Change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [X] 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

Since the flag is set to true by default, the existing integration tests
should work as it is.

src/main/java/io/pinecone/configs/PineconeConfig.java

@@ -52,6 +52,7 @@ public class PineconeConfig {
     private String sourceTag;
     private ProxyConfig proxyConfig;
     private ManagedChannel customManagedChannel;
+    private boolean enableTLS = true;
 
     /**
      * Constructs a {@link PineconeConfig} instance with the specified API key.
@@ -207,6 +208,24 @@ public String getUserAgent() {
         return buildUserAgent();
     }
 
+    /**
+     * Returns true if TLS is enabled or false otherwise.
+     *
+     * @return enableTls
+     */
+    public boolean isTLSEnabled() {
+        return enableTLS;
+    }
+
+    /**
+     * Sets whether TLS is enabled.
+     *
+     * @param enableTLS true to enable TLS, false to disable it.
+     */
+    public void setTLSEnabled(boolean enableTLS) {
+        this.enableTLS = enableTLS;
+    }
+
     private String buildUserAgent() {
         String userAgent = String.format("lang=java; %s=%s", "pineconeClientVersion", pineconeClientVersion);
         if (this.getSourceTag() != null && !this.getSourceTag().isEmpty()) {

src/main/java/io/pinecone/configs/PineconeConnection.java

@@ -136,13 +136,21 @@ private void onConnectivityStateChanged() {
 
     private ManagedChannel buildChannel() {
         String endpoint = formatEndpoint(config.getHost());
-        NettyChannelBuilder builder = NettyChannelBuilder.forTarget(endpoint);
+        NettyChannelBuilder builder = NettyChannelBuilder
+                .forTarget(endpoint)
+                .userAgent(config.getUserAgent());
 
         try {
-            builder = builder.overrideAuthority(endpoint)
-                    .negotiationType(NegotiationType.TLS)
-                    .sslContext(GrpcSslContexts.forClient().build())
-                    .userAgent(config.getUserAgent());
+            if(config.isTLSEnabled()) {
+                builder = builder
+                        .overrideAuthority(endpoint)
+                        .negotiationType(NegotiationType.TLS)
+                        .sslContext(GrpcSslContexts.forClient().build());
+            }
+            else {
+                builder = builder
+                        .negotiationType(NegotiationType.PLAINTEXT);
+            }
 
             if(config.getProxyConfig() != null) {
                 ProxyDetector proxyDetector = getProxyDetector();