Make doctools optional

2 jobs for master in 29 minutes and 18 seconds (queued for 123 minutes and 22 seconds)
Status Name Job ID Coverage
  Build
failed build_clazy_clang_tidy #103269

00:09:54

passed linux kf5-qt5 qt5.15 #103268

00:19:24

41.0%
 
Name Stage Failure
failed
build_clazy_clang_tidy Build
[ 92%] Linking CXX executable ../../bin/akonadi_imap_resource
[ 92%] Built target akonadi_imap_resource
make: *** [Makefile:160: all] Error 2
Uploading artifacts for failed job
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1