Add function for cache_clear

[BobcatProgrammer]

Problem/Motivation

I want to trigger a clearing of the adguard cache, as I'm using dyndns for my services and need to clear cache if my public IP changes (optimistic caching is enabled). I want to use that functionality downstream in the homeassistant core component for adguard

Expected behavior

Have a function to call that part of the api

Actual behavior

Not implemented

Steps to reproduce

None

Proposed changes

I propose adding a function to call the cache_clear endpoint. From the adguard openapi docs:

curl -X 'POST' \
  'https://editor.swagger.io/control/cache_clear' \
  -H 'accept: */*' \
  -d ''

I prepared a PR for this #1094