Use spring-boot-starter-parent in spring-batch-geode

[scordio]

Similar to #159, #163, and #165, this PR:

• Uses the spring-boot-starter-parent to keep all the dependency and plugin versions aligned
• Uses the flatten-maven-plugin with ossrh flatten mode to strip all the unnecessary details from the final POM

Flattened POM

<?xml version="1.0" encoding="UTF-8"?>
<!--
  ~ Copyright 2022 the original author or authors.
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~       https://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  -->
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.springframework.batch.extensions</groupId>
  <artifactId>spring-batch-geode</artifactId>
  <version>0.1.0-SNAPSHOT</version>
  <name>Spring Batch Geode</name>
  <description>Spring Batch extension for Apache Geode</description>
  <url>https://github.com/spring-projects/spring-batch-extensions/tree/main/spring-batch-geode</url>
  <licenses>
    <license>
      <name>Apache-2.0</name>
      <url>https://www.apache.org/licenses/LICENSE-2.0.txt</url>
      <distribution>repo</distribution>
    </license>
  </licenses>
  <scm>
    <connection>git://github.com/spring-projects/spring-batch-extensions.git</connection>
    <developerConnection>git@github.com:spring-projects/spring-batch-extensions.git</developerConnection>
    <url>https://github.com/spring-projects/spring-batch-extensions</url>
  </scm>
  <dependencies>
    <dependency>
      <groupId>org.springframework.batch</groupId>
      <artifactId>spring-batch-core</artifactId>
      <version>4.3.10</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.data</groupId>
      <artifactId>spring-data-geode</artifactId>
      <version>2.7.18</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>
</project>

[scordio]

As I understand from https://github.com/spring-projects/spring-data-geode, the project is in maintenance mode, so Spring Boot 2 is probably the highest version we can reach.