Content modifier processor should allow to set timestamp

**Is your feature request related to a problem? Please describe.**
I tried to replace a Regex parser with a Content modifier processor (see #11688) but that is not able to set the timestamp.

**Describe the solution you'd like**
Content modifier should support setting the timestamp with the time_key and related parameters like the Regex parser.

**Describe alternatives you've considered**
Finally I implemented that in Lua but that requires Lua extensions.

**Additional context**
That came up while experimenting with the solutions described in #11687.