Expand the unattended upgrade install process to allow for installation of plugins and additional configuration

Problem Definition

The unattended upgrade will allow for the installer responses to be automated, however once the instance is setup there's no automated configuration after this.

Suggested Solution

Provide a method to use a pre-existing database configuration and install certain plugins after install.

Workaround

One sample workaround would be to script this, for example:

1. Create another database and copy the data from the existing one.
2. Download the standalone installer.
3. Install it with the pre-answered responses.
4. Stop the instance.
5. Edit the server.xml as appropriate.
6. Update dbconfig.xml with the new database.
7. Populate $JIRA_HOME/plugins/installed-plugins with the required plugins.
8. Start up the instance, which will then upgrade the data (or simply start with it), and enable the plugins.