Add some more extrapolation in h5parm freqs
Another try at https://jira.skatelescope.org/browse/AST-468, previously wrongly implemented in !24 (merged). The problem was the abs: the tolerance was applied also to the right of the start of the first frequency in the h5parm. This was caught by tapplycalh5/testampl4 in DP3.
I'm still working on a test of GetFreqIndex here.