sql: implement pg_stat tables where possible

[rafiss]

Add implementations for the following tables, for the columns that can be supported in CockroachDB

• pg_statistic
• pg_statistic_ext_data
• pg_stats
• pg_stats_ext

Jira issue: CRDB-10219

[otan]

reltuples in pg_class has a similar affliction. this prevent AWS DMS from providing "estimates" of progress.

example query:

2022-12-08 19:04:34 UTC:172.31.55.39(37296):postgres@replicationload:[666]:LOG:  statement: BEGIN;declare "SQL_CUR0x146ee0196860" cursor with hold for 
	 ( 
	  select
	     t.schemaname                  as ownerName,
	     t.tablename                   as tableName,
	     /*c.oid*/ cast(c.oid as bigint) as objectId, 
	     (select n_live_tup from pg_stat_user_tables s where s.schemaname=t.schemaname and s.relname=t.tablename)  as row_count,
		   1						as tableType
	  from pg_tables t, pg_class c, pg_namespace n
	  /*where clause number 1 (table where clause)*/
	  where t.tablename=c.relname
	  and   n.oid	   = c.relnamespace
	  and   t.schemaname = n.nspname
	  and t.schemaname <> 'information_schema'
	  and t.tablename  <> 'awsdms_ddl_audit'
	  and t.tablename  <> 'awsdms_heartbeat'
	  and
	  (
	     (( (1=0) ) -- Explicit Inclusion
	     or 
	     (
	        ( 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'good\_table'
	 ) -- Patterned Inclusion
	          and not
	        ( 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_changes%'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_apply%'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_truncation%'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_audit\_table'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_status'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_suspended\_tables'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_history'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_validation\_failure'
	 or 
	 t.schemaname LIKE '%' and t.schemaname not like 'pg\_%' and t.tablename LIKE 'awsdms\_cdc\_%awsdms\_full\_load\_exceptions%'
	 ) -- Patterned exclusion
	      ))
	      and 
	      (1=1) 
	  )
	
	  UNION
	
	  select
	     v.schemaname                  as ownerName,
	     v.viewname                   as tableName,
	     /*c.oid*/ cast(c.oid as bigint) as objectId, 
	     0  as row_count,/**/ 
		   2						as tableType
	  from pg_views v, pg_class c, pg_namespace n
	  /*where clause number 2 (view where clause)*/ 
	  where v.viewname = c.relname
	  and   n.oid	    = c.relnamespace
	  and   v.schemaname = n.nspname
	  and v.schemaname <> 'information_schema'
	  and v.viewname  <> 'awsdms_ddl_audit'
	  and v.viewname  <> 'awsdms_heartbeat'
	  and
	  (
	     (( (1=0) ) -- Explicit Inclusion
	     or 
	     (
	        ( (1=0) ) -- Patterned Inclusion
	          and not
	        ( (1=0) ) -- Patterned exclusion
	      ))
	      and 
	      (1=1) 
	  )
	 )
	 order by 1,2
	;fetch 10000 in "SQL_CUR0x146ee0196860"