Include FlagEmbedding in pyproject dependencies

[sarvesh211999]

It would be very useful if FlagEmbdding version can be added as dependency in pyprojec.toml, so that after upgrading pymilvus-models we are not left with breaking changes due to FlagEmbdding being upgraded

[wxywb]

This is a hard choice to make, if someone only uses openai or voyage's model, then he doesn't need to download a bunch of dependencies introduced by FlagEmbedding. By the way, I'll check some alternative methods to solve this problem.