fix(docs): add Spider as a webpage loader (#32453)
[Spider](https://spider.cloud/) is a webpage loader and should be listed
under the
["Webpages"](https://python.langchain.com/docs/integrations/document_loaders/#webpages)
table on the Document loaders page.
Twitter: https://x.com/WilliamEspegren
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Co-authored-by: Mason Daugherty <mason@langchain.dev>
