feat: add Jina Embeddings

[JoanFM]

Description

I added a JinaEmbeddings class to enable the use of Jina Embeddings from their API

How Has This Been Tested?

from dbgpt.rag.embedding.embeddings import JinaEmbeddings
embs = JinaEmbeddings(api_key=<your_key>) 
ret = embs.embed_documents(['hey here', 'hey there'])
print(ret)

Checklist:

• My code follows the style guidelines of this project
• I have already rebased the commits and make the commit message conform to the project standard.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• Any dependent changes have been merged and published in downstream modules

[csunny]

@JoanFM Thanks for your PR， we will make a test and merge it.

[Aries-ckt]

LGTM

[yihong0618]

Do we need to add some docs?

[JoanFM]

Do we need to add some docs?

I could not find the place where to put them.

[fangyinc]

Do we need to add some docs?

Aha, we will update this document after the RAG document is completed.

[fangyinc]

LGTM.

[Aries-ckt]

r+