minor #7263 Fix sample sqlite database path in doctrine config (chalasr)

This PR was merged into the 3.1 branch.

Discussion
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Fix sample sqlite database path in doctrine config

I think sqlite databases should be stored in `var/` as it is storage.
About the `%kernel.data_dir%` removed here, I never heard about such a parameter in the core, either I missed it or it's very old.
Please tell me if we should first change it on lower branches, replacing it by `%kernel.root_dir%/app/data/data.sqlite`.

See also symfony/symfony-standard#1032 on the same topic

Commits
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9126fdf Fix sample sqlite database path in doctrine config

Author: xabbuh

reference/configuration/doctrine.rst

@@ -203,7 +203,7 @@ Full Default Configuration
                         password="secret"
                         driver="pdo_mysql"
                         driver-class="MyNamespace\MyDriverImpl"
-                        path="%kernel.data_dir%/data.sqlite"
+                        path="%kernel.root_dir%/../var/data/data.sqlite"
                         memory="true"
                         unix-socket="/tmp/mysql.sock"
                         wrapper-class="MyDoctrineDbalConnectionWrapper"
@@ -431,7 +431,7 @@ The following block shows all possible configuration keys:
                     password="secret"
                     driver="pdo_mysql"
                     driver-class="MyNamespace\MyDriverImpl"
-                    path="%kernel.data_dir%/data.sqlite"
+                    path="%kernel.root_dir%/../var/data/data.sqlite"
                     memory="true"
                     unix-socket="/tmp/mysql.sock"
                     wrapper-class="MyDoctrineDbalConnectionWrapper"