Add content purge filter

[johngian]

This filter can be added in case ALL content in a certain time range needs to be purged.

[johngian]

I pinned the jsonc-parser dependency only for dev-dependencies so CI can work. (This is the last known version that works with node 12)

[johngian]

Just tested it locally. Other than some minor changes on the configuration for start/end time (initial example mentioned unix timestamps but it expected iso8601 strings) it worked OK.