SQL: Match naming conventions for asciidoc files (elastic/x-pack-elasticsearch#3471)

SQL's asciidoc files were all named `sql-the-thing.asciidoc` but our
standard is to name asciidoc files `the-thing.asciidoc` and keep them in
appropriate directories.

relates elastic/x-pack-elasticsearch#3182

Original commit: elastic/x-pack-elasticsearch@ab81763ffd

docs/en/sql/endpoints/index.asciidoc

@@ -0,0 +1,4 @@
+include::rest.asciidoc[]
+include::translate.asciidoc[]
+include::cli.asciidoc[]
+include::jdbc.asciidoc[]

docs/en/sql/endpoints/sql-endpoints.asciidoc

@@ -1,4 +0,0 @@
-include::sql-rest.asciidoc[]
-include::sql-translate.asciidoc[]
-include::sql-cli.asciidoc[]
-include::sql-jdbc.asciidoc[]

docs/en/sql/index.asciidoc

@@ -25,9 +25,9 @@ indices and return tabular results. There are four main components:
     A JDBC driver for Elasticsearch.
 --
 
-include::sql-getting-started.asciidoc[]
+include::getting-started.asciidoc[]
-include::endpoints/sql-endpoints.asciidoc[]
+include::endpoints/index.asciidoc[]
-include::functions/sql-functions.asciidoc[]
+include::functions/index.asciidoc[]
-include::language/sql-language.asciidoc[]
+include::language/index.asciidoc[]
 
 :jdbc-tests!:

docs/en/sql/language/index.asciidoc

@@ -4,6 +4,6 @@
 This chapter describes the SQL syntax and data types supported in X-Pack.
 As a general rule, the syntax tries to adhere as much as possible to ANSI SQL to make the transition seamless.
 
-include::sql-data-types.asciidoc[]
+include::data-types.asciidoc[]
-include::sql-syntax.asciidoc[]
+include::syntax.asciidoc[]
-include::sql-reserved.asciidoc[]
+include::reserved.asciidoc[]