Update release note and version number (microsoft#4471)

Release Note (microsoft#4284)

Fix PAI virtualCluster in non-reuse mode (microsoft#4061)

update readme (microsoft#3827)

Co-authored-by: Scarlett Li <[email protected]>
Co-authored-by: kvartet <[email protected]>
Co-authored-by: --help <[email protected]>

v2.2 release

change v2.0 to v2.1 (microsoft#3443)

Add release note for v2.0 (microsoft#3291)

v1.9 tag

Release v1.8

Upgrade pai restful API (microsoft#2722)