(#13274) linters: Add annotations for YAML lint + add schema verification for config.yml and conandata.yml

* first attempt at a yaml linter wit github actions output

* This is less strict but has more information

* fixup message

* run config linter in Action

* better ux feedback

* try to use newlines

https://github.com/actions/toolkit/issues/193#issuecomment-605394935

* clean up

* fixup file name

* trying custom class for quoted str

* underlying yaml parser does not keep quotes

* trying to catch ints as problems

* remove test code

* and to "linter testing"

* install deps

* run new linter unconditionally

* revert testing changes

* new script for conandata (this one is much harder to spec)

* debugging

* lets see all the errors

* yamale -s ../linter/config_yaml_schema.yml aaf/config.yml

from linters folder as a test

* adjust script to match meeting discussion

* make sure the docs and linters match

* fix link

* Update conandata.yml

* exit 1 is not needed with annotations

* add annotation matchers for yaml since those do do much

* fix search for type

* fix whitespace

* tryout a yamllint file with a better looking matcher

* copy syntax from readme

* test if it's running in the wrong dir 🤔

* try with debug output

* bump since i dont have permissions

* bump - dont glob star

* bump

* less star globs

* also add action to conandata way

* bump

* drop action for cli + matcher

* more docs around linters

* fix file and name

* cleanup

docs/developing_recipes_locally.md

@@ -124,6 +124,52 @@ It is possible to run the linter locally the same way it is being run [using Git
   pylint --rcfile=linter/pylintrc_testpackage recipes/fmt/all/test_package/conanfile.py
   ```
 
+## Running the YAML Linters
+
+There's two levels of YAML validation, first is syntax and the second is schema.
+The style rules are located in [`linter/yamllint_rules.yml`](../linter/yamllint_rules.yml) and are used to ensure consistence.
+The [`config.yml](how_to_add_packages.md#configyml) is required for the build infrastructure and the
+[`conandata.yml` patch fields](conandata_yml_format.md#patches-fields) have required elements that are enforced with
+schema validation. There's are to encourage the best possible quality of recipes and make reviewing faster.
+
+### Yamllint
+
+* (Recommended) Use a dedicated Python virtualenv.
+* Ensure you have required tools installed: `yamllint` (better to uses fixed versions)
+
+  ```sh
+  pip install yamllint==1.28
+  ```
+
+* Now you just need to execute the `yamllint` commands:
+
+  ```sh
+  # Lint a recipe:
+  yamllint --config-file linter/yamllint_rules.yml -f standard recipes/fmt/all/conanfile.py
+
+  # Lint the test_package (same command)
+  yamllint --config-file linter/yamllint_rules.yml -f standard recipes/fmt/all/test_package/conanfile.py
+  ```
+
+### Yamlschema
+
+* (Recommended) Use a dedicated Python virtualenv.
+* Ensure you have required tools installed: `strictyaml` and `argparse` (better to uses fixed versions)
+
+  ```sh
+  pip install strictyaml==1.16 argparse==1.4
+  ```
+
+* Now you just need to execute the validation scripts:
+
+  ```sh
+  # Lint a config.yml:
+  python3 linter/config_yaml_linter.py recipes/fmt/config.yml
+
+  # Lint a conandata.yml
+  python3 linter/conandata_yaml_linter.py recipes/fmt/all/conandata.yml
+  ```
+
 ## Testing the different `test_*_package`
 
 This can be selected when calling `conan create` or separately with `conan test`