community: add ZoteroRetriever (#30270)

**Description** 
This contribution adds a retriever for the Zotero API.
[Zotero](https://www.zotero.org/) is an open source reference management
for bibliographic data and related research materials. A retriever will
allow langchain applications to retrieve relevant documents from
personal or shared group libraries, which I believe will be helpful for
numerous applications, such as RAG systems, personal research
assistants, etc. Tests and docs were added.

The documentation provided assumes the retriever will be part of the
langchain-community package, as this seemed customary. Please let me
know if this is not the preferred way to do it. I also uploaded the
implementation to PyPI.

**Dependencies**
The retriever requires the `pyzotero` package for API access. This
dependency is stated in the docs, and the retriever will return an error
if the package is not found. However, this dependency is not added to
the langchain package itself.

**Twitter handle**
I'm no longer using Twitter, but I'd appreciate a shoutout on
[Bluesky](https://bsky.app/profile/koenigt.bsky.social) or
[LinkedIn](https://www.linkedin.com/in/dr-tim-k%C3%B6nig-534aa2324/)!


Let me know if there are any issues, I'll gladly try and sort them out!

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/packages.yml

@@ -526,4 +526,9 @@ packages:
   provider_page: dell
 - name: langchain-tavily
   path: .
-  repo: tavily-ai/langchain-tavily
+  repo: tavily-ai/langchain-tavily
+- name: langchain-zotero-retriever
+  path: .
+  repo: TimBMK/langchain-zotero-retriever
+  name_title: Zotero
+  provider_page: zotero