[WIP] Add release guide for XTable

[vinishjail97]

Important Read

• Please ensure the GitHub issue is mentioned at the beginning of the PR

What is the purpose of the pull request

Add the release guide/process for Apache XTable, the guide has been added based on the guidelines provided by Apache. https://infra.apache.org/release-publishing https://www.apache.org/legal/release-policy.html

Special guidelines for incubating projects. https://incubator.apache.org/guides/releasemanagement.html#best-practice https://infra.apache.org/release-publishing.html#uploading

Brief change log

(for example:)

• Added release guide
• Added scripts for generating GPG keys
• Added scripts for deploying jars and artifacts signed by the GPG keys

Verify this pull request

This pull request is a release guide without any test coverage, the guide will be run in a dry-run mode to ensure everything is working as expected before merging the change to main branch.