[Feature][integration][Java] Java Implementation of Vector Store with Elasticsearch Support

[twosom]

Search before asking

• [x] I searched in the issues and found nothing similar.

Description

Following the design proposal in #143, we need to implement Java version of Vector Store functionality to enable RAG (Retrieval-Augmented Generation) capabilities in Flink Agents. This issue focuses on implementing the core Vector Store infrastructure and Elasticsearch-based vector store as the first implementation.

Are you willing to submit a PR?

• [x] I'm willing to submit a PR!