Add cli_lint_errors_count to java (#1820)

In order to parse the amount of errors Checkstyle finds, we need to tell
the parser which type of message the linter responds with.
In case of checkstyle, it has a message like Checkstyle ends with
([0-9]+) errors which corresponds to `regex_number`. Otherwise
megalinter will respond always with 1.

megalinter/descriptors/java.megalinter-descriptor.yml

@@ -32,6 +32,7 @@ linters:
       - sarif
       - -o
       - "{{SARIF_OUTPUT_FILE}}"
+    cli_lint_errors_count: "regex_number"
     cli_lint_errors_regex: "Checkstyle ends with ([0-9]+) errors"
     cli_version_extra_args:
       - "-jar"