* Add inital 1.9.0 release note

Add inital 1.9.0 release note, will update later if there are
more items to add.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update notes/coredns-1.9.0.md
Co-authored-by: Chris O'Haver <cohaver@infoblox.com>
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update notes/coredns-1.9.0.md
Co-authored-by: Chris O'Haver <cohaver@infoblox.com>
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update notes/coredns-1.9.0.md
Co-authored-by: Chris O'Haver <cohaver@infoblox.com>
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Update version string to 1.9.0
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
Co-authored-by: Chris O'Haver <cohaver@infoblox.com>