Move the TAG definition of each example to the corresponding
source file (previously it is defined in the common example
intialization header file), which can avoid the redefinition
of TAG in some situations.
Since the scripts of CI will bypass common_components when
trying to get ALL_EXAMPLES, and these BLE Mesh components
will only be used by other mesh examples, i.e. no need to
be compiled as a single example, so we rename the folder
to common_componnets.
