Make the Solr port configurable / auto-select a free port if 8983 is in use

[markkerzner]

Problem

Solr's port is hardcoded to 8983. On machines where another program already uses 8983 (or a
policy blocks it), Solr can't bind and the whole review side fails — with no easy remedy for
the user.

Ask

• Make the Solr port configurable (a setting / env var), and/or
• Auto-detect a free port if 8983 is taken, and have FreeEedUI/the engine use the chosen port.

Notes

Search/index config, the Control Panel, and FreeEedUI's Solr client all need to read the same
configured port rather than assuming 8983. Especially valuable on locked-down institutional
machines. Related: the "surface Solr start failure" issue.