Enforce consistent and correct toml formatting (#2518)

Using taplo, fixes all our broken and inconsistent toml formatting and
adds CI to keep them tidy.

If people want we can customise the format rules as described here
https://taplo.tamasfe.dev/configuration/formatter-options.html

@ggwpez, I suggest zepter is used only for checking features are
propagated, and leave formatting for taplo to avoid duplicate work and
conflicts.

TODO
- [x] Use `exclude = [...]` syntax in taplo file to ignore zombienet
tests instead of deleting the dir

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Bastian Köcher <git@kchr.de>

.gitlab/pipeline/check.yml

@@ -90,6 +90,16 @@ check-rust-feature-propagation:
     - cargo install --locked --version 0.13.3 -q -f zepter && zepter --version
     - zepter run check
 
+check-toml-format:
+  stage: check
+  extends:
+    - .kubernetes-env
+    - .common-refs
+  script:
+    - cargo install taplo-cli --locked --version 0.8.1
+    - taplo format --check --config .config/taplo.toml
+    - echo "Please run `taplo format --config .config/taplo.toml` to fix any toml formatting issues"
+
 # More info can be found here: https://github.com/paritytech/polkadot/pull/5865
 .check-runtime-migration:
   stage: check