Move citus views into the public schema

Currently Citus defines eight views that report various information about the cluster. One of these views (`citus_tables`) is defined in the `public` schema which makes it easily discoverable for users by simple things like tab completion in a psql session:

```
awolk=# select * from citus
citus. citus_internal. citus_tables
awolk=#
```

It would be nice to move the remaining 7 views into the public schema for consistency and better discoverability.

```
awolk=# \dv
List of relations
Schema | Name | Type | Owner
--------+--------------+------+-------
public | citus_tables | view | awolk
(1 row)

awolk=# \dv pg_catalog.citus*
List of relations
Schema | Name | Type | Owner
------------+-------------------------------+------+-------
pg_catalog | citus_dist_stat_activity | view | awolk
pg_catalog | citus_lock_waits | view | awolk
pg_catalog | citus_shard_indexes_on_worker | view | awolk
pg_catalog | citus_shards | view | awolk
pg_catalog | citus_shards_on_worker | view | awolk
pg_catalog | citus_stat_activity | view | awolk
pg_catalog | citus_stat_statements | view | awolk
(7 rows)

awolk=# \dv citus*
List of relations
Schema | Name | Type | Owner
------------+-------------------------------+------+-------
pg_catalog | citus_dist_stat_activity | view | awolk
pg_catalog | citus_lock_waits | view | awolk
pg_catalog | citus_shard_indexes_on_worker | view | awolk
pg_catalog | citus_shards | view | awolk
pg_catalog | citus_shards_on_worker | view | awolk
pg_catalog | citus_stat_activity | view | awolk
pg_catalog | citus_stat_statements | view | awolk
public | citus_tables | view | awolk
(8 rows)
```