Two changes:
 * Create a file to signal success
 * Only sleep on previous failure if explicitly requested by the chart

This solves two issues.

If init containers are started again for a running env due to e.g.
the cluster being restarted, `install-mediawiki` will simply succeed
and return instead of getting stuck for an hour in the sleep command.

Also, by default do not sleep and simply fail if a previous run
didn't succeed. The container will only sleep if explicitly requested
via `debug.initContainers`

Bug: T379358