fix: SignInButton issue with AsgardeoV2

[brionmario]

Purpose

This pull request introduces improvements to documentation and refines logic for handling platform-specific flows in the Asgardeo React SDK. The most notable changes include an update to the README.md to recognize contributors, enhanced checks for embedded sign-in flows, and a fix in the provider logic for Asgardeo V2 platform support.

Documentation update:

• Added a "Contributors" section to README.md to acknowledge project contributors and visually display contributor avatars.

Platform-specific logic improvements:

• Updated the conditional in AsgardeoReactClient.ts to check that the argument is an object and not empty before executing the embedded sign-in flow for Platform.AsgardeoV2, preventing unintended flow execution.
• Imported the isEmpty utility from @asgardeo/browser in AsgardeoReactClient.ts to support the improved conditional logic.
• Fixed the conditional in AsgardeoProvider.tsx so that branding preferences are skipped only for Platform.AsgardeoV2, aligning with platform capabilities and the related issue tracker.

Code cleanup:

• Removed unused import of Platform from embedded-flow.ts, streamlining the codebase.

Related Issues

• feat: provide initiate provision for asgardeo/thunder runtime #212

Related PRs

• feat: add asagrdeo/thunder support ⚡️ #213

Checklist

• Followed the CONTRIBUTING guidelines.
• Manual test round performed and verified.
• Documentation provided. (Add links if there are any)
• Unit tests provided. (Add links if there are any)

Security checks

• Followed secure coding standards in http://wso2.com/technical-reports/wso2-secure-engineering-guidelines?
• Confirmed that this PR doesn't commit any keys, passwords, tokens, usernames, or other secrets?

[asgardeo-github-bot]

🦋 Changeset detected

The changes in this PR will be included in the next version bump.

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