[ADF-1586] Added Core services docs (#2582)

docs/cookie.service.md

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+# Cookie service
+
+Stores key-value data items as browser cookies.
+
+## Methods
+
+`getItem(key: string): string | null` <br/>
+Gets an item identified by `key`.
+
+` setItem(key: string, data: string, expiration: Date | null, path: string | null): void ` <br/>
+Stores an item under `key`.
+
+## Details
+
+This service uses browser [cookies](https://en.wikipedia.org/wiki/HTTP_cookie)
+to store data in the form of key-value pairs. An optional `expiration` date can be
+supplied for the cookie and a `path` can be used to reduce the chances of name
+clashes with cookies from other sources.
+
+Cookies have a storage size limit that varies between browsers but is often around
+4KB. Consider using [web storage](storage.service.md) if you need to store data
+beyond this size.
+
+<!-- Don't edit the See also section. Edit seeAlsoGraph.json and run config/generateSeeAlso.js -->
+<!-- seealso start -->
+## See also
+
+- [Storage service](storage.service.md)
+<!-- seealso end -->