This change implements lazy loading of individual hooks for providers
manager. First the hooks list is discovered by the manager when
hooks are accessed, but the hooks are not immediately
imported - the hooks initially keep just a callable that will
be used to retrieve the hook when first accessed.

Besides listing details of all hooks, all Hooks are only imported when we
want to retrieve the list of available field behaviours and widgets
(which only happens in webserver and should happen anyway whenever one
of those are needed because they are all collectively used in the
connection view).

In the case when hooks are accessed in tasks
(connection.get_hook()) only the individual Hooks are
imported when accessed.

The chand deprecates 'hook-class-names' json-schema and replaces it
with 'connection-types' because we need to know connection-type
for each HookClass name declaratively so that we can utilse
it in connection.get_hook() mehtod (otherwise we do not know
which Hooks conrrespond to which connection type without importing
them.

The change is backwards compatible. It adds deprecation
warnings in case providers use the 'hook-class-names' property
only and log warnings in case it provides both `hook-class-names`
and `connection-types` but there are inconsistencies between
those.

Part of this change is also to fix some inconsistencies found
when all hooks were added to connection-types arrays, which
make potetntially backwards-incompatible changes to Google Provider
where some hooks were useing `google_cloud_default` name for
default_connection_type, but they were in fact using different,
specialized Hook.