Add documentation for SpEL support.

Closes #1719

Author: schauder

src/main/antora/modules/ROOT/nav.adoc

@@ -11,6 +11,7 @@
 ** xref:commons/custom-conversions.adoc[]
 ** xref:repositories/custom-implementations.adoc[]
 ** xref:repositories/core-extensions.adoc[]
+** xref:value-expressions.adoc[]
 ** xref:query-by-example.adoc[]
 ** xref:repositories/core-domain-events.adoc[]
 ** xref:commons/entity-callbacks.adoc[]

src/main/antora/modules/ROOT/pages/value-expressions.adoc

@@ -0,0 +1 @@
+include::{commons}@data-commons::page$value-expressions.adoc[]

src/main/antora/modules/ROOT/partials/mapping.adoc

@@ -23,6 +23,9 @@ class MyEntity {
 }
 ----
 
+You may use xref:value-expressions.adoc[Spring Data's SpEL support] to dynamically create the table name.
+Once generated the table name will be cached, so it is dynamic per mapping context only.
+
 [[entity-persistence.custom-column-name]]
 == Override column names
 
@@ -82,6 +85,10 @@ class MySubEntity {
 ----
 endif::[]
 
+You may use xref:value-expressions.adoc[Spring Data's SpEL support] to dynamically create column names.
+Once generated the names will be cached, so it is dynamic per mapping context only.
+
+
 ifdef::embedded-entities[]
 
 [[entity-persistence.embedded-entities]]