hideal2pds outputs a label where SAMPLE_BITS value is always 16

[tgiroux]

ISIS version(s) affected: 4.2.0

Description

When a user selects bits=8, the SAMPLE_BITS value in the output label should be 8. For all other cases (bits=9-16), SAMPLE_BITS should be 16. At present it is 16 for all cases including bits=8.

How to reproduce

In isis/src/mro/apps/hideal2pds/tsts/differentBitCompressions run $make output and check output/output8.pvl to see that SAMPLE_BITS=16

Possible Solution

Include the following code within IsisMain() of main.cpp for hideal2pds:
if( nbits == 8 ) {
image.addKeyword(PvlKeyword("SAMPLE_BITS", toString(nbits)), Pvl::Replace);
}

Additional context

Related to #3978 by @audiefen