Added new guide for using index templates with the low-level client

[Djcarrillo6]

Description

This file is a comprehensive guide on how to use index templates with the OpenSearch .NET client. It targets the OpenSearch.Net low-level client and provides a variety of examples that demonstrate how to create, retrieve, delete, and use index templates in different scenarios. The file also includes important notes on the state of both low & high level clients at the time it was written.

The key sections of the guide include:
• Setup: Instructions for setting up a connection to an OpenSearch server running on the local machine.
• Index Template API Actions: Details on how to interact with the Index Template API to create and use index templates that match certain patterns. It demonstrates scenarios of using single and multiple templates, and how template priority affects the settings applied.
• Composable Index Templates: Information about the newer type of template, composable index templates, which allow for composing multiple component templates into a final one.
• Get an Index Template: Guidance on how to retrieve specifications of a particular index template.
• Delete an Index Template: Steps to delete a specified index template.
• Cleanup: Demonstrates how to delete created indices and templates for clean-up.

The actual coding examples are in C#, involving the OpenSearch.Net client. Code blocks provided illustrate how various API actions like PutTemplateForAll, PutTemplateV2ForAll, PutComponentTemplate, GetTemplateForAll, and DeleteTemplateForAll are used. The guide should be updated in future when new features or methods become available in the high level OpenSearch client.

Issues Resolved

Part of #187

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[Xtansia]

Hi @Djcarrillo6, thanks for working on this!

I've just got some points for how to cleanup the code samples a bit, and make sure they're correct.

[Djcarrillo6]

Hi @Xtansia, thanks so much for the detailed suggestions! I believe I accepted each of your suggested changes but let me know if any are missing or if there is anything else you'd like me to change.