Custom reloptions for table AM

Let table AM define custom reloptions for its tables. This allows specifying
AM-specific parameters by the WITH clause when creating a table.

The reloptions, which could be used outside of table AM, are now extracted
into the CommonRdOptions data structure.  These options could be by decision
of table AM directly specified by a user or calculated in some way.

The new test module test_tam_options evaluates the ability to set up custom
reloptions and calculate fields of CommonRdOptions on their base.

The code may use some parts from prior work by Hao Wu.

Discussion: https://postgr.es/m/CAPpHfdurb9ycV8udYqM%3Do0sPS66PJ4RCBM1g-bBpvzUfogY0EA%40mail.gmail.com
Discussion: https://postgr.es/m/AMUA1wBBBxfc3tKRLLdU64rb.1.1683276279979.Hmail.wuhao%40hashdata.cn
Reviewed-by: Reviewed-by: Pavel Borisov, Matthias van de Meent, Jess Davis

src/backend/access/heap/heaptoast.c

@@ -32,6 +32,13 @@
 #include "access/toast_internals.h"
 #include "utils/fmgroids.h"
 
+/*
+ * HeapGetToastTupleTarget
+ *      Returns the heap relation's toast_tuple_target.  Note multiple eval of argument!
+ */
+#define HeapGetToastTupleTarget(relation, defaulttarg) \
+		((HeapRdOptions *) (relation)->rd_options ? \
+		((HeapRdOptions *) (relation)->rd_options)->toast_tuple_target : (defaulttarg))
 
 /* ----------
  * heap_toast_delete -
@@ -174,7 +181,7 @@ heap_toast_insert_or_update(Relation rel, HeapTuple newtup, HeapTuple oldtup,
 		hoff += BITMAPLEN(numAttrs);
 	hoff = MAXALIGN(hoff);
 	/* now convert to a limit on the tuple data size */
-	maxDataLen = RelationGetToastTupleTarget(rel, TOAST_TUPLE_TARGET) - hoff;
+	maxDataLen = HeapGetToastTupleTarget(rel, TOAST_TUPLE_TARGET) - hoff;
 
 	/*
 	 * Look for attributes with attstorage EXTENDED to compress.  Also find