Consider including geotiff submodule as core

[cappelletto]

Current geotiff submodule is stable enough to be use across the whole codebase (at organization level). However, there is no need to keep it as submodule for tiff2png, if we prefer a standalone solution.

CI/CD (including ctests) coul benefit from a more monolithic branch, where geotiff is migrated as part of the core modules. If necessary, switching back to a submodule is a trivial task