server: allow customizing the default repo filter hgweb has the (undocument) configuration option web.view that allows restricting visible revisions to immutable. This is useful for serving the same storage as publishing and non-publishing repo. Add the new server.view option to serve the same purpose by changing the default behavior of `getdispatchrepo`. Drop the hard-coded 'served' filter in the batch handler of v1 of the wire proto, this is a left-over from the days before `getdispatchrepo` existed. Differential Revision: https://phab.mercurial-scm.org/D5946