Feature request: Add a grok processor

**Is your feature request related to a problem? Please describe.**
When I use regular expressions to process data, it is often cumbersome and not very user-friendly.

**Describe the solution you'd like**
I hope to add a grok processor to simplify this process.

The issue names no files, tests, or entry points. Start by identifying how existing regular-expression processors are organized, then define the supported grok syntax, expected inputs and outputs, and acceptance tests before implementing the feature.

Written by the indexing model from the issue text.