Add check for filename template values

[jerinpetergeorge]

Type of PR - Enhancement

Description

This PR will check whether the values of DBBACKUP_FILENAME_TEMPLATE and DBBACKUP_MEDIA_FILENAME_TEMPLATE contains any "slashes" (/) in it (Ref: #479 ).

Why should this be added

If the filename contains slashes, the storage will create a directory out of it and the --clean flag won't work as expected.