Add shadow spring namespace example and adjust template

[totalo]

For #12366.

Changes proposed in this pull request:

• add shardingsphere-jdbc-memory-local-shadow-spring-namespace-jdbc-example
• add shardingsphere-jdbc-memory-local-shadow-spring-namespace-mybatis-example
• add shardingsphere-jdbc-memory-local-shadow-spring-namespace-jpa-example
• adjust template

[codecov-commenter]

Codecov Report

Merging #13954 (550ae80) into master (c13972c) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master   #13954   +/-   ##
=========================================
  Coverage     63.41%   63.41%           
  Complexity     1765     1765           
=========================================
  Files          2806     2806           
  Lines         41738    41738           
  Branches       7128     7128           
=========================================
  Hits          26470    26470           
  Misses        13244    13244           
  Partials       2024     2024           

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