Align with entity naming best practice (#2201)

See:
https://cap.cloud.sap/docs/guides/domain-modeling#naming-conventions
There are plenty of entity names in examples in this CDL topic. Some of
them are "real" in that they are genuine representations such as Orders
and Products. These should be subject to the naming convention best
practice of being pluralised.

Others are clearly illustrative only, such as the Foo, Bar, Baz set and
those conveying meaning for the given example such as EmployeeView,
SomeView, P, Proj, SomeExposedEntity and so on. These should not be
subject to the naming convention.

Note: Perhaps we should add something to the naming convention section
itself to qualify the boundary of where it applies, i.e. "mostly" at the
schema level, less so at the service definition level?

Author: qmacro

cds/cdl.md

@@ -639,7 +639,7 @@ type Complex {
 If the element has an enum type, you can use the enum symbol instead of a literal value:
 ```cds
 type Status : String enum {open; closed;}
-entity Order {
+entity Orders {
   status : Status default #open;
 }
 ```
@@ -650,7 +650,7 @@ entity Order {
 If you want to base an element's type on another element of the same structure, you can use the `type of` operator.
 
 ```cds
-entity Author {
+entity Authors {
   firstname : String(100);
    lastname : type of firstname; // has type "String(100)"
 }
@@ -685,7 +685,7 @@ For string types, declaration of actual values is optional; if omitted, the actu
 
 ```cds
 type Gender : String enum { male; female; non_binary = 'non-binary'; }
-entity Order {
+entity Orders {
   status : Integer enum {
     submitted =  1;
     fulfilled =  2;
@@ -1916,14 +1916,14 @@ exposing entities.
 
 ```cds
 service CatalogService {
-  entity Product as projection on data.Products {
+  entity Products as projection on data.Products {
     *, created.at as since
   } excluding { created };
 }
 service MyOrders {
   //> $user only implemented for SAP HANA
-  entity Order as select from data.Orders { * } where buyer=$user.id;
-  entity Product as projection on CatalogService.Product;
+  entity Orders as select from data.Orders { * } where buyer=$user.id;
+  entity Products as projection on CatalogService.Products;
 }
 ```
 
@@ -2096,7 +2096,7 @@ Within service definitions, you can additionally specify `actions` and `function
 
 ```cds
 service MyOrders {
-  entity Order { /*...*/ };
+  entity Orders { /*...*/ };
   // unbound actions / functions
   type cancelOrderRet {
     acknowledge: String enum { succeeded; failed; };