Fix Sponsors buttons (#3616)

* Fix Sponsors buttons

Due to limitations in the number of GitHub Sponsors buttons (there can be only up to 4 buttons), part of the team is ignored.

This replaces the buttons with our "Sponsorship" page and a button to sponsor `log4j-core` via Tidelift.

* Add warning about `github` key

Author: ppkarwasz

Diff for: .github/FUNDING.yml

@@ -19,12 +19,7 @@
 # For details see:
 # https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/displaying-a-sponsor-button-in-your-repository
 #
-# This list includes in the same order, committers of Log4j listed on:
-# https://logging.apache.org/support.html#sponsors
-github:
-  - carterkozak
-  - garydgregory
-  - jvz
-  - ppkarwasz
-  - rgoers
-  - vy
+# WARNING: the `github` key accepts only 4 GitHub user ids, so we can not use this feature.
+#
+custom: "https://logging.apache.org/support.html#sponsors"
+tidelift: "maven/org.apache.logging.log4j:log4j-core"