codegen-java: Support not annotating constructor parameters (#792)

Motivation:
Spring Boot configuration classes neither require nor benefit from annotating constructor parameters with their name.
The same is true for pkl-config-java configuration classes compiled with `-parameter`.

Changes:
- Change CLI parameter `--params-annotation` to accept a `none` value.
  This is recommended in https://clig.dev/#arguments-and-flags and is how the `-F` parameter of the `ssh` command works.
- Change `paramsAnnotation` property in Gradle plugin, CliJavaCodeGeneratorOptions, and JavaCodegenOptions as follows:
  - Change meaning of `null` from "generate org.pkl.java.config.mapper.Named annotations" to "do not generate annotations".
    This is a breaking change (only) affecting users who explicitly set the property to `null` instead of omitting it.
  - Change property default from `null` to:
    `null` if `generateSpringBootConfig` is `true` and `org.pkl.java.config.mapper.Named` otherwise
- add tests
- update docs of this and other codegen options

Result:
Generated code does not contain unnecessary annotations.

pkl-gradle/src/main/java/org/pkl/gradle/PklPlugin.java

@@ -192,6 +192,15 @@ public class PklPlugin implements Plugin<Project> {
 
           spec.getGenerateGetters().convention(false);
           spec.getGenerateJavadoc().convention(false);
+          // Not using `convention()` so that users can disable generation of
+          // constructor parameters annotations by setting this property to `null`.
+          spec.getParamsAnnotation()
+              .set(
+                  project.provider(
+                      () ->
+                          spec.getGenerateSpringBootConfig().get()
+                              ? null
+                              : "org.pkl.config.java.mapper.Named"));
 
           createModulesTask(JavaCodeGenTask.class, spec)
               .configure(