community : allow using apikey for PubMedAPIWrapper (#27246)
**Description**:
> Without an API key, any site (IP address) posting more than 3 requests
per second to the E-utilities will receive an error message. By
including an API key, a site can post up to 10 requests per second by
default.
quoted from A General Introduction to the E-utilities,NCBI :
https://www.ncbi.nlm.nih.gov/books/NBK25497/
I have simply added a api_key parameter to the PubMedAPIWrapper that can
be used to increase the number of requests per second from 3 to 10.
**Twitter handle** : @KORmaori
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Co-authored-by: Erick Friis <erick@langchain.dev>
