Maintenance:

• Removed code to be able to start up MapProxy without PIL.

Fixes:

• Add python-dateutil dependency to avoid errors on startup.
• Add ogcapi to config-schema.json to avoid warnings on startup.

What's Changed

• feat: remove no PIL compatibility by @simonseyock in #1321
• OGCAPI related fixes by @rouault in #1337
• dev: prepare 6.0.1 release by @simonseyock in #1338

Full Changelog: 6.0.0...6.0.1