Create and bundle Keystore Initialization JSP file for Confluence 5.8+

This is a continuation of CONF-11074. The keystore initialization files in CONF-11074 no longer work for Confluence 5.8 or higher, including special versions for customers migrating from Atlassian Cloud to self-hosted Confluence Server (e.g. version OD-5.8).

This is problematic because all instances exported from Confluence Cloud have empty KEYSTORE tables (due to CONF-28954), and without a way to initialize the keystore this means we can expect all Cloud to Server migrated instances to have broken applinks. For example, JIRA gadgets added to a Confluence page will not load correctly without a populated keystore.

Ideally the permanent fix is to resolve CONF-28954 and also to ensure Confluence can never get to a position where the KEYSTORE table is empty. Short of that, the next best thing is create a new initialization file to populate the keystore like we have done before, bundle it with Confluence, and incorporate a health check looking for missing keystore entries.