Describe the plugin's data table export functionality (#362)

Author: bmuschko

docs/reference/gradle-plugin-configuration.md

@@ -47,10 +47,11 @@ The `rewrite` DSL exposes a few configuration options:
 * `activeRecipe` - Explicitly turns on recipes by name (the name given in the `specs.openrewrite.org/v1beta/recipe` resource). No recipe is run unless explicitly turned on with this setting.
 * `activeStyle` - Explicitly turns on a style by name (the name given in the `specs.openrewrite.org/v1beta/style` resource). No style is applied unless explicitly turned on with this setting.
 * `configFile` - Where to look for an OpenRewrite YML configuration file somewhere in the project directory (or really anywhere on disk). This file is not required to exist. If not specified otherwise, the default value is `<project directory>/rewrite.yml`.
+* `exportDatatables` - Boolean flag toggling whether the plugin should export the data tables generated by the active recipes. The default is `false`. The resulting files can be found in the directory `<build directory>/reports/rewrite/datatables/<timestamp>`.
 * `failOnDryRunResults` - Boolean flag toggling whether `rewriteDryRun` should throw an exception and non-zero exit code if changes are detected. The default is `false`.
 * `sizeThresholdMb` - Threshold over which non-Java sources are ignored during parsing. The default threshold is 10Mb.
 * `exclusion` - One or more paths, relative to the project the plugin is applied to, where non-Java sources are ignored during parsing. Supports [glob patterns](https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/nio/file/FileSystem.html#getPathMatcher\(java.lang.String\)).
-*   `plainTextMasks` - A set of file masks to denote which files should be parsed as plain text. Evaluated as a [PathMatcher](https://docs.oracle.com/javase/8/docs/api/java/nio/file/PathMatcher.html) glob pattern, where "\*\*" matches any number of directories and "\*" matches a single directory or filename. **Exclusions take precedence over any plain text masks.** If this configuration is not explicitly defined the default masks are:
+* `plainTextMasks` - A set of file masks to denote which files should be parsed as plain text. Evaluated as a [PathMatcher](https://docs.oracle.com/javase/8/docs/api/java/nio/file/PathMatcher.html) glob pattern, where "\*\*" matches any number of directories and "\*" matches a single directory or filename. **Exclusions take precedence over any plain text masks.** If this configuration is not explicitly defined the default masks are:
 
     ```bash title="Default masks"
     **/META-INF/services/**