feat: add mongoDB changset example

[Sonichigo]

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Description

• Please describe your changes:
  This pull request introduces a new documentation page, "Get Started with Changelogs," to guide users on how to define and manage changelogs for SQL and MongoDB in Harness Database DevOps. The page includes detailed examples of changelogs for both database types, showcasing schema changes, indexing, and sample data management.

  • SQL Changelog Examples: The page provides YAML examples for SQL changelogs, demonstrating how to create tables, add indexes, insert sample data, and define rollback operations.

  • MongoDB Changelog Examples: Similarly, the page includes YAML examples for MongoDB changelogs, showcasing operations like creating collections, adding indexes (including unique and compound indexes), and managing context-specific changes.

• Jira/GitHub Issue numbers (if any): https://harness.atlassian.net/browse/DBOPS-1327

• Preview links/images (Internal contributors only): __________________

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[bot-gitexp-user]

Please check the Execution Link of the Pipeline for the Website Draft URL. This is located in the Preview Step behind the Harness VPN and also is available in #hdh_alerts. E.g Website Draft URL: https://unique-id--harness-developer.netlify.app. Current Draft URL is: https://68763720742ace12b054173e--harness-developer.netlify.app

[stephenatwell]

Thoughts on showing the validator syntax that works as well, since it should save folks time? Here's a working example:
- createCollection:
collectionName: pets
options: '{"validator": {"$jsonSchema": {"bsonType": "object", "required":["name","species"]},"properties":{"name":{"bsonType": "string","description": " The Name"},"species":{"bsonType": "string","description": "cat, dog, or other"}}},"validationAction": "warn","validationLevel":"strict"}'