Merge branch '365-cache-shows-old-extension-version-after-upload' into 'develop'

Add flushing caches after successful extension import

Closes #365

See merge request !373
4 jobs for 366-oops-an-error-occurred-on-https-extensions-typo3-org-extension-event in 7 minutes and 19 seconds
Status Job ID Name Coverage
  Test
passed #9633
test:php

00:00:21

passed #9632
test:unit

00:01:53

 
  Build
passed #9634
build

00:01:32

 
  Layout
passed #9635
layout

00:03:52