Add upgrade notice post-install script to RPM spec file

[jtpalmer]

Description

Adds a post-install script to the RPM spec file that outputs some text if the RPM is being upgraded.

Motivation and Context

After upgrading the xdmod RPM the xdmod-upgrade must be executed. This is currently not done automatically because it may take hours to run or require user interaction. This addition is intended to remind users to run this command.

Tests performed

Upgraded RPM and checked for the new message. Also did a clean install of the RPM to confirm the message is not displayed in that situation.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project as found in the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.