FDO#80652 (part) help for page CMIS file access

This commit adds a help button to CMIS dialog

Change-Id: Ic4f826c4ee5fa31a94e3d22974a0e13bf460a249
Reviewed-on: https://gerrit.libreoffice.org/11801
Reviewed-by: Olivier Hallot <olivier.hallot@edx.srv.br>
Tested-by: Olivier Hallot <olivier.hallot@edx.srv.br>