Docs: switch to EasyCLA, clarify Git email setup, fix links and build instructions #1

[Manideep285]

Motivation

• Update contributor documentation to reflect FINOS' migration to EasyCLA and provide clear guidance for contributors on signing and authorizing CLA checks.
• Reduce PR rejections by clarifying how to configure the Git commit email so CLA checks can correctly identify contributors.
• Fix missing/placeholder links and small typos and make the local site build instructions explicit and actionable.

Description

• Replaced references to the legacy "CLA Bot" with EasyCLA and added instructions on how to authorize and sign as an individual through the PR UI.
• Clarified Git email troubleshooting with explicit commands such as git config user.email, git config --global user.email ID+myusername@users.noreply.github.com, git commit --amend, git reset --soft, and git rebase.
• Corrected and added URLs and placeholders (including the Legend Studio URL, fork URL, and GitHub/email links) and fixed minor typos such as "recommeded" to "recommended".
• Updated documentation build instruction to reference the build-site.sh script and ensured the example workflow includes git commands and npm run start for the local dev server.

Testing

• Built the documentation site locally using ./scripts/build-site.sh and started the dev server with npm run start, and the site rendered without build errors.
• No automated unit tests apply to these documentation changes beyond the local build, and no test failures were observed.

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[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Manideep285 / name: Manideep (51d3a64, 6eae2bf)