Prepare for 8.7.0 (gazebosim#2671)

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Prepare for 9.0.0 release (gazebosim#2635)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Update readme, changelog and prepare for 9.0.0pre1 release (gazebosim…

…#2554)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Prepare for 7.9.0 release (gazebosim#2534)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Prepare for 8.6.0 release (gazebosim#2496)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Do not include merge-forward in changelog

Signed-off-by: Jose Luis Rivero <jrivero@osrfoundation.org>

Prepare for 8.5.0 (gazebosim#2455)

Signed-off-by: Benjamin Perseghetti <bperseghetti@rudislabs.com>

Prepare for 8.4.0 release (gazebosim#2442)

Signed-off-by: Ian Chen <ichen@openrobotics.org>

Prepare for 8.3.0 (gazebosim#2368)

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

Prepare for 8.2.0 (gazebosim#2335)

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>