Update CHANGELOG for 8.2.6 release
Update CHANGELOG for 8.2.6 release

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jirutka/gitlabhq,jirutka/gitlabhq,LUMC/gitlabhq,dreampet/gitlab,mr-dxdy/gitlabhq,LUMC/gitlabhq,icedwater/gitlabhq,screenpages/gitlabhq,icedwater/gitlabhq,dreampet/gitlab,darkrasid/gitlabhq,icedwater/gitlabhq,htve/GitlabForChinese,shinexiao/gitlabhq,LUMC/gitlabhq,screenpages/gitlabhq,Soullivaneuh/gitlabhq,darkrasid/gitlabhq,t-zuehlsdorff/gitlabhq,openwide-java/gitlabhq,daiyu/gitlab-zh,dplarson/gitlabhq,allysonbarros/gitlabhq,dreampet/gitlab,darkrasid/gitlabhq,iiet/iiet-git,t-zuehlsdorff/gitlabhq,Soullivaneuh/gitlabhq,axilleas/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,martijnvermaat/gitlabhq,iiet/iiet-git,screenpages/gitlabhq,htve/GitlabForChinese,SVArago/gitlabhq,dplarson/gitlabhq,shinexiao/gitlabhq,openwide-java/gitlabhq,htve/GitlabForChinese,mr-dxdy/gitlabhq,stoplightio/gitlabhq,mr-dxdy/gitlabhq,stoplightio/gitlabhq,allysonbarros/gitlabhq,dplarson/gitlabhq,martijnvermaat/gitlabhq,allysonbarros/gitlabhq,screenpages/gitlabhq,martijnvermaat/gitlabhq,openwide-java/gitlabhq,mmkassem/gitlabhq,daiyu/gitlab-zh,SVArago/gitlabhq,jirutka/gitlabhq,Soullivaneuh/gitlabhq,axilleas/gitlabhq,iiet/iiet-git,t-zuehlsdorff/gitlabhq,mr-dxdy/gitlabhq,shinexiao/gitlabhq,axilleas/gitlabhq,daiyu/gitlab-zh,htve/GitlabForChinese,Soullivaneuh/gitlabhq,mmkassem/gitlabhq,SVArago/gitlabhq,iiet/iiet-git,LUMC/gitlabhq,dreampet/gitlab,t-zuehlsdorff/gitlabhq,daiyu/gitlab-zh,shinexiao/gitlabhq,allysonbarros/gitlabhq,openwide-java/gitlabhq,axilleas/gitlabhq,dplarson/gitlabhq,darkrasid/gitlabhq,icedwater/gitlabhq,stoplightio/gitlabhq,martijnvermaat/gitlabhq,stoplightio/gitlabhq,mmkassem/gitlabhq,SVArago/gitlabhq