chore: remove multi-modules and example stub (#39)

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<!-- Provide a brief summary of the changes -->

Removes the example stub and organizes repo as single gradle project.

## Description
<!-- Provide a detailed description of the changes -->

It seems there is difficulty in publishing a single module of a
multi-module project using the nexus plugin. Since the examples module
is currently just a stub, this change just removes that module and makes
this project a single gradle project.

We can add the example as a separate directory later and pull the
starter dependency from maven as the java SDK does.

## References
<!-- Provide a list of any applicable references here (GitHub Issue,
[OpenFGA RFC](https://github.com/openfga/rfcs), other PRs, etc..) -->

gradle-nexus/publish-plugin#84

## Review Checklist
- [x] I have clicked on ["allow edits by
maintainers"](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/allowing-changes-to-a-pull-request-branch-created-from-a-fork).
- [ ] I have added documentation for new/changed functionality in this
PR or in a PR to [openfga.dev](https://github.com/openfga/openfga.dev)
[Provide a link to any relevant PRs in the references section above]
- [x] The correct base branch is being used, if not `main`
- [ ] I have added tests to validate that the change in functionality is
working as expected

build.gradle

@@ -1,5 +1,9 @@
 plugins {
-    id 'java'
+    id 'java-library'
+    id 'org.springframework.boot' version "${springBootVersion}" apply false
+    id 'io.spring.dependency-management' version "${springDependencyManagementVersion}"
+
+    // quality
     id 'com.diffplug.spotless' version '6.25.0'
     id 'jacoco'
 
@@ -9,6 +13,43 @@ plugins {
     id 'io.github.gradle-nexus.publish-plugin' version '1.3.0'
 }
 
+apply from: 'publish.gradle'
+
+java {
+    sourceCompatibility = 17
+    targetCompatibility = 17
+
+    withJavadocJar()
+    withSourcesJar()
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencyManagement {
+    imports {
+        mavenBom org.springframework.boot.gradle.plugin.SpringBootPlugin.BOM_COORDINATES
+    }
+}
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot'
+    implementation 'org.springframework.boot:spring-boot-autoconfigure'
+    implementation 'org.springframework.boot:spring-boot-starter-security'
+
+    api 'dev.openfga:openfga-sdk:0.4.0'
+
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    testImplementation 'org.springframework.security:spring-security-test'
+    testImplementation 'org.hamcrest:hamcrest:2.2'
+    testImplementation 'org.mockito:mockito-core:5.11.0'
+}
+
+test {
+    useJUnitPlatform()
+}
+
 subprojects {
     apply plugin: 'java'
     apply plugin: 'com.diffplug.spotless'

settings.gradle

@@ -1,4 +1 @@
-rootProject.name = 'fga-spring-boot-starter'
-
-include 'openfga-spring-boot-starter'
-include 'examples:servlet'
+rootProject.name = 'openfga-spring-boot-starter'