[ci] Using lychee for doxygen link checking
Using lychee for doxygen link checking. Is much faster (12 vs 30 minutes, https://gitlab.opengeosys.org/ogs/ogs/-/jobs/405441) and even faster with hot cache (< 1 minute, https://gitlab.opengeosys.org/ogs/ogs/-/jobs/405447). Keeping old job for some time to check if the new one works reliable.
Edited by Lars Bilke