Update Geo/AS field documentation to indicate deference to plugin

Update the schema documentation for the `..._as_*` and `..._geo_*` fields to indicate they should not be extracted from messages when that data exists, that they should instead use the `vendor_` prefix to avoid field collisions.

Also provide clarity in the AS number field data type, considering the value may include the text prefix "AS".

Start by locating the schema documentation entries for the `..._as_*` and `..._geo_*` fields. Review the AS number field's current data type and update the documentation so existing data defers to the plugin, extracted alternatives use the `vendor_` prefix, and values with the `AS` text prefix are clearly described.

Written by the indexing model from the issue text.