docs: add README for Agent agentflow node

[AbdullahBapra]

Added README documentation explains how the Agent node works, its main features, and how to use it in a flow. It also includes clear descriptions of parameters and expected behavior, making it easier for developers to understand and integrate this node into their projects.

The goal is to improve the overall documentation quality and help both new and existing users work with agentflow more efficiently.

[gemini-code-assist]

Code Review

This pull request introduces a new README documentation for the Agent component, detailing its parameters, features, and licensing information. A suggestion was made to update the license link to reference the 'main' branch instead of 'master' for consistency with the repository's primary branch.

[gemini-code-assist]

The license link uses the master branch, but the repository's primary branch is main (as referenced in other documentation files like packages/agentflow/README.md).

Suggested change

	Source code in this repository is made available under the [Apache License Version 2.0](https://github.com/FlowiseAI/Flowise/blob/master/LICENSE.md).
	Source code in this repository is made available under the [Apache License Version 2.0](https://github.com/FlowiseAI/Flowise/blob/main/LICENSE.md).

[HenryHengZJ]

feel free to add it to our docs :)