Update Tidelift docs with latest campaign

Tidelift has launched a new marketing campaign as outlined here:

* https://forum.tidelift.com/t/task-enhancement-marketing-the-tidelift-subscription-to-your-users/321

This PR splits the previous "sponsor" information into two, Open Collective
and Tidelift (as they have very different target audiences).

Also took the opportunity to reorder some items at the end of
the contents page in a manner that I believe make more sense.

doc/en/sponsor.rst

@@ -8,18 +8,6 @@ compensation when possible is welcome to justify time away from friends, family
 Money is also used to fund local sprints, merchandising (stickers to distribute in conferences for example)
 and every few years a large sprint involving all members.
 
-If you or your company benefit from pytest and would like to contribute to the project financially,
-we are members of two online donation platforms to better suit your needs.
-
-Tidelift
---------
-
-`Tidelift`_ aims to make Open Source sustainable by offering subscriptions to companies which rely
-on Open Source packages. This subscription allows it to pay maintainers of those Open Source
-packages to aid sustainability of the work.
-
-You can help pytest and the ecosystem by obtaining a `Tidelift subscription`_.
-
 OpenCollective
 --------------
 
@@ -32,7 +20,6 @@ monthly donations directly to the project.
 See more datails in the `pytest collective`_.
 
 
-
 .. _Tidelift: https://tidelift.com
 .. _Tidelift subscription: https://tidelift.com/subscription/pkg/pypi-pytest
 .. _Open Collective: https://opencollective.com