Update root readme adding key features, repo structure details, user uide reference, jira reference, details for repo clarity.

[sumobrian]

Description

Objective: Revise the root README.md file of the opensearch-migrations project to provide a comprehensive overview and detailed documentation, enhancing clarity and usability for users and contributors. Provide references to other READMEs in the repo.

Tasks Completed:

• Rename the Title.
• Add a Detailed Table of Contents.
• Update the Overview Section.
• Identify Key Features.
• Update Supported Versions and Platforms.
• Add Issue Tracking Information.
• Detail the Project Structure.
• Include a reference to User Guide.
• Add Getting Started Instructions.
• Reorignize the Development Section.
• Update Contributing Guidelines.
• Detail Publishing Instructions
• Add Acknowledgments.
• Remove Release Section.
• Correct Spelling and Grammar Errors.
• Improve Formatting and Consistency.
• Enhance Readability.
• Verify External References.

Issues Resolved

JIRA MIGRATIONS-2081

Is this a backport? If so, please add backport PR # and/or commits #

Testing

Verified links do not return 404s and that targets work as expected. The gradle targets need to be updated. Ideally gradlew build would build the complete solution. I opened a bug to make this change.

Check List

• [ ] New functionality includes testing
  • [ ] All tests pass, including unit test, integration test and doctest
• [ ] New functionality has been documented
• [x] Commits are signed per the DCO using --signoff

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.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.19%. Comparing base (0b08287) to head (564ea9c). Report is 25 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1066 +/- ## ============================================ + Coverage 80.16% 80.19% +0.02% - Complexity 2744 2863 +119 ============================================ Files 367 383 +16 Lines 13743 14333 +590 Branches 949 988 +39 ============================================ + Hits 11017 11494 +477 - Misses 2149 2245 +96 - Partials 577 594 +17 ``` | [Flag](https://app.codecov.io/gh/opensearch-project/opensearch-migrations/pull/1066/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project) | Coverage Δ | | |---|---|---| | [gradle-test](https://app.codecov.io/gh/opensearch-project/opensearch-migrations/pull/1066/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project) | `78.21% <ø> (+0.13%)` | :arrow_up: | | [python-test](https://app.codecov.io/gh/opensearch-project/opensearch-migrations/pull/1066/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project) | `90.24% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=opensearch-project#carryforward-flags-in-the-pull-request-comment) to find out more.

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