Consider scoping citus_tables / citus_shards views to current_user's permissions

Instead of emitting such warnings, skipping the tables / schemas that the current_user doesn't have permission to view might be a better idea. From a user perspective, I wouldn't expect such warnings.

I believe Postgres also does some filtering based on "current_user" for some of its views.

Reproducible on 11.3 too.

```sql
CREATE SCHEMA my_schema;
CREATE TABLE my_schema.my_table (id int);

SELECT create_distributed_table('my_schema.my_table', 'id', shard_count => 4);

CREATE ROLE test_non_super_user WITH LOGIN;
ALTER ROLE test_non_super_user NOSUPERUSER;

\c - test_non_super_user

table citus_tables;
WARNING: permission denied for schema my_schema
WARNING: could not connect to localhost:9701 to get size of table "my_table"
┌────────────────────┬──────────────────┬─────────────────────┬───────────────┬────────────┬─────────────┬─────────────┬───────────────┐
│ table_name │ citus_table_type │ distribution_column │ colocation_id │ table_size │ shard_count │ table_owner │ access_method │
├────────────────────┼──────────────────┼─────────────────────┼───────────────┼────────────┼─────────────┼─────────────┼───────────────┤
│ my_schema.my_table │ distributed │ id │ 1 │ │ 4 │ onurctirtir │ heap │
└────────────────────┴──────────────────┴─────────────────────┴───────────────┴────────────┴─────────────┴─────────────┴───────────────┘
(1 row)

table citus_shards;
WARNING: permission denied for schema my_schema
WARNING: permission denied for schema my_schema
┌────────────────────┬─────────┬───────────────────────────┬──────────────────┬───────────────┬───────────┬──────────┬────────────┐
│ table_name │ shardid │ shard_name │ citus_table_type │ colocation_id │ nodename │ nodeport │ shard_size │
├────────────────────┼─────────┼───────────────────────────┼──────────────────┼───────────────┼───────────┼──────────┼────────────┤
│ my_schema.my_table │ 102008 │ my_schema.my_table_102008 │ distributed │ 1 │ localhost │ 9701 │ │
│ my_schema.my_table │ 102009 │ my_schema.my_table_102009 │ distributed │ 1 │ localhost │ 9702 │ │
│ my_schema.my_table │ 102010 │ my_schema.my_table_102010 │ distributed │ 1 │ localhost │ 9701 │ │
│ my_schema.my_table │ 102011 │ my_schema.my_table_102011 │ distributed │ 1 │ localhost │ 9702 │ │
└────────────────────┴─────────┴───────────────────────────┴──────────────────┴───────────────┴───────────┴──────────┴────────────┘
(4 rows)

```

Start with the SQL reproduction in the issue and inspect the implementations of the citus_tables and citus_shards views. Compare their visibility behavior with PostgreSQL's current_user filtering. Done means users without permission no longer receive warnings or rows for inaccessible schemas, while permitted rows remain available.

Written by the indexing model from the issue text.