Introduce credential-store.sh

Currently there is just delivered wildfly-elytron-tool.jar in $EAP_HOME/bin folder. I think for convenience it would be better if it will contain also credential-store.sh script, although now it will be just java -jar wildfly-elytron-tool.jar credential-store

• It saves space on command line
• It is analogous to vault.sh - so obvious when looking for credential store tool
• With such script we gain customization point for credential store. As wildfly-elytron-tool.jar will expand, it is possible some credential-store customization for starting tool will be necessary
• Once wildlfy elytron tool will be exposed with modules, script can be updated to start with modules with no change for user