modules/pre-commit: make rawConfig option type recursively updatable

[yunfachi]

lib.types.attrs does not recursively update attribute values. It simply overwrites them. Because of this behavior, the code on line 427 does not allow setting own rawConfig.repos at all:

    rawConfig =
      {
        repos =
          [
            {
              repo = "local";
              hooks = processedHooks;
            }
          ];
      } // lib.optionalAttrs (cfg.excludes != [ ]) {
        exclude = mergeExcludes cfg.excludes;
      } // lib.optionalAttrs (cfg.default_stages != [ ]) {
        default_stages = cfg.default_stages;
      };

[yunfachi]

ping @domenkozar