Because we need to remain backwards compatible with the old
`dust-threshold` value we set the default value for
`channel-max-fee-exposure` later in the program flow. Given
the restrictions of the sample config check we need to exclude
this value from the check.
The new script perfoms the following checks on the sample-lnd.conf file:
1. Checks that all relevant options of lnd are included.
2. Verifies that defaults are labeled if there are also further examples.
3. Checks that all default values of lnd --help are mentioned correctly,
including empty defaults and booleans which are set to false by
default.
