Upgrade main-next to Apache Geode 1.15 snapshots.

[jxblum]

Prepare the main-next branch to build Spring Data for Apache Geode (SDG) 2.6/Q (and beyond) on Apache Geode 1.15 (build) snapshots.

Adapt SDG to any API changes in Apache Geode 1.15.

[jxblum]

This upgrade is dependent on the following GEODE JIRA tickets:

• https://issues.apache.org/jira/browse/GEODE-9629
• https://issues.apache.org/jira/browse/GEODE-9630

This upgrade (task) will only be completed once the GEODE JIRA tickets referenced above are resolved, meaning the changes have been merged to the Apache Geode 1.15 development branch and Apache Geode 1.15 bits (snapshots) are available with these changes for SDG to consume.