Modify License documentation where applicable

[cvvergara]

License GPL-2.0 is deprecated move to GPL-2.0 -or-later

TODO (if applicable):

• pgRouting
• pgRoutingLayer
• osm2pgRouting
• Website
• workshop
• docker-pgRouting
• osm2pgrouting4qgis
• any other sub product that I might have forgotten

References:
pgRouting/pgrouting#1851
https://www.gnu.org/licenses/identify-licenses-clearly.en.html
https://spdx.org/licenses/GPL-2.0+.html

[dkastl]

According to the link you posted, the GNU General Public License v2.0 or later seems to be deprecated actually: https://spdx.org/licenses/GPL-2.0+.html ... so what is the currently "valid" one? It's a bit confusing. I don't think we want to change to one that is already deprecated, no?

[dkastl]

Sorry, I missunderstood ... we want to move to this one: https://spdx.org/licenses/GPL-2.0-only.html

[dkastl]

I think at the time GNU General Public License v2.0 or later was selected, the idea was to also reference GPL v3.0.

So if we now change this to GNU General Public License v2.0 only, then we actually make a restricition that was not intended.

What would actually happen, if we would make a change to GNU General Public License v3.0 or later instead?

[dkastl]

This is an interesting question https://opensource.stackexchange.com/questions/7993/is-it-legal-to-fork-gpl-2-or-later-software-and-make-gpl-2-only-changes

[dkastl]

Maybe one consequence of changing to only could be, that this will make it impossible to use code in GPLv3 https://www.gnu.org/licenses/gpl-faq.en.html#AllCompatibility