Allow custom columns reports

Currently the tabular report modes (I.e. csv, pretty,markdown) each use a different fixed set of columns.

Trippy should be enhanced to support a user specified list of custom columns in these report modes.

Trippy does already allows for custom columns to be specified but only in Tui. See https://github.com/fujiapple852/trippy/issues/757.

Note that the json report includes most (but not all, some columns like the last sequence number do not make sense to show in a final snapshot report) custom columns and likely does not require this enhancement.