fix(userguide): proof chapter introduction

related to #CAM-2258
doc(ldap) posixGroupMode

related to #CAM-2281
Merge branch 'master' of github.com:camunda/docs.camunda.org
fix(userguide): proofread and correct

is related to #CAM-2257
chore(caseDefinition/REST): provide docs about exposed CaseDefinitionQuery

related to CAM-2199
chore(enterprise): update download page for 7.1.2