The parameter max_htlc_value_in_flight_msat stablished by peers on
channel opening (BOLT02) can now be retrived from the
gossmods_from_listpeerchannels API.
Adapted the corresponding callback functions in renepay and askrene to
take into account that value as a constraint to the value we can send
through a channel.
Changelog-Add: fetch max_htlc_value_in_flight_msat from gossmods_listpeerchannels API
Signed-off-by: Lagrang3 <lagrang3@protonmail.com>