Pre-validate config

Certain configuration mistakes still cause rather unhelpful error messages, because we validate the config after normalizing it, so errors during normalization aren't cleanly handled.

Case in point, I just accidentally did this

#kaocha/v1
{:tests {:id :cljs
         :type :kaocha.type/cljs}}

Which should have been

#kaocha/v1
{:tests [{:id :cljs :type :kaocha.type/cljs}]}

Which gave me this error

Execution error (IllegalArgumentException) at meta-merge.core/meta-merge (core.cljc:100).
Don't know how to create ISeq from: clojure.lang.Keyword

Full report at:
/tmp/clojure-7895642946752562024.edn

This one's a bit annoying because we do have specs for config maps, but they only apply after normalization, adding defaults, renaming non-qualified keys etc. We'll need seperate specs (or a different validation strategy) if we want to validate the raw tests.edn.

Reproduce the malformed tests.edn configuration and trace the existing config specs and normalization step. Determine how raw configuration can be validated before normalization, then confirm that the example produces a clear validation error instead of the meta-merge exception.