The lib input plugin could expect the data comes in a free string

**Is your feature request related to a problem? Please describe.**
When I use the lib plugin to ingest data manually, I have to parse the message first by myself, and rewrite it in a JSON format to pass it using flb_lib_push(). However, the flexible and powerful parser config of fluent-bit attracts me very much. For example, in the "tail", it has very friendly configurable parser. Is it possible to make flb_lib_push() to support parser config? Thank you.
**Describe the solution you'd like**
The lib plugin can be configurable with parser.
**Describe alternatives you've considered**
**Additional context**