For single page crawls:
- Always force 1 browser to be used, ignoring browser windows/scale
setting
- Don't use custom PVC volumes in crawler / redis, just use emptyDir -
no chance of crawler being interrupted and restarted on different
machine for a single page.
Adds a 'is_single_page' check to CrawlConfig, checking for either limit
or scopeType / no extra hops.
Fixes#2655