Prepare 9.0.0 release (apache#2714)

Prepare 9.0.0 release (apache#2714)

update verification script and add notes on signing keys (apache#2520)

update verification script and add notes on signing keys (apache#2520)

update verification script and add notes on signing keys (apache#2520)

Prepare for datafusion 8.0.0 , ballista 0.7.0 release (apache#2490)

* bump versions

* changelog 7.0.0 to 8.0.0

* update versions in docs

* revert changelog

* re-generate changelogs

* revert ballista changelog

* update version missed by script and update script

* regenerate ballista changelog with correct version

Prepare for 7.x release: Update version to 7.1.0, add ChangeLog (apac…

…he#2187)

* Update version

* modify script to respect release branch

* Create changelog for release

* manually fix changelog

* Apply suggestions from code review

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Co-authored-by: Andrew Lamb <andrew@nerdnetworks.org>

Fix verification scripts for 7.0.0 release (apache#1830)

* Update release and verify scripts

* fixup

* Fix publish check

* remove python check

Fix verification scripts for 7.0.0 release (apache#1830)

* Update release and verify scripts

* fixup

* Fix publish check

* remove python check

create datafusion 6.0.0, ballista 0.6.0 and python 0.4.0 releases (ap…

…ache#1253)

* create datafusion 6.0.0, ballista 0.6.0 and python 0.4.0 releases