Add sensory memory documentation

[Shekharrajak]

Linked issue: #350

Purpose of change

This PR adds comprehensive documentation for the Sensory Memory feature in Flink Agents. The documentation covers:

• Overview and key characteristics of Sensory Memory
• When to use Sensory Memory vs other memory types
• Access methods and API usage (Python and Java)
• Practical usage examples
• Auto-cleanup behavior and lifecycle
• Comparison with Short-Term and Long-Term Memory
• Best practices and anti-patterns

The documentation follows the existing documentation style and provides clear guidance for developers using Sensory Memory in their agents.

Tests

Documentation changes do not require code tests. The documentation was verified by:

• Reviewing existing documentation style and format
• Ensuring code examples match the actual API implementation
• Validating that all referenced concepts align with the codebase

API

This change does not touch any public APIs. It is documentation-only.

Documentation

• doc-needed

• doc-not-needed

[wenjin272]

Hi, @Shekharrajak, thanks for your great work.

The document for sensory memory and long-term memory in #402 is detailed and clear. But Memory as an integrated functional module may require a dedicated documentation section. We could add a new "Memory" chapter under "Development," and in its overview, explain the characteristics and use cases of different types of Memory. Then, specific details can be covered in separate subsections such as Sensory & Short-Term Memory(sensory memory is same with short-term memory in api, we can introduce them in same section) and Long-Term Memory.

Currently, I introduce the short-term memory in Workflow Agent section, you can move and merge it to Sensory & Short-Term Memory section.