fix: Grabbing a user key? Provider/Resource docs wrong, module wrong, NR

[JiwaniZakir]

Fixes #2863

The key attribute in website/docs/r/api_access_key.html.markdown was documented as returning "the actual API key", misleading users into expecting the full, unobfuscated value. Due to a NerdGraph API limitation, the returned value is always obfuscated. Updates the attribute description to clarify it returns an obfuscated value (e.g., NRAK-XXXXXXXXXX) and that the full key is not retrievable via this provider.

[CLAassistant]

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