[release][website] Add release notes for Release 2.1.0 (#2292)
[release][website] Add release notes for Release 2.1.0 (#2292)


ArvinDevel/incubator-pulsar,merlimat/pulsar,jai1/pulsar,nkurihar/pulsar,ArvinDevel/incubator-pulsar,yahoo/pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,ArvinDevel/incubator-pulsar,nkurihar/pulsar,yahoo/pulsar,massakam/pulsar,nkurihar/pulsar,jai1/pulsar,yahoo/pulsar,ArvinDevel/incubator-pulsar,nkurihar/pulsar,ArvinDevel/incubator-pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,massakam/pulsar,jai1/pulsar,merlimat/pulsar,jai1/pulsar,nkurihar/pulsar,nkurihar/pulsar,jai1/pulsar,nkurihar/pulsar,nkurihar/pulsar,jai1/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,massakam/pulsar,merlimat/pulsar,ArvinDevel/incubator-pulsar,nkurihar/pulsar,jai1/pulsar,massakam/pulsar,yahoo/pulsar,merlimat/pulsar,jai1/pulsar,jai1/pulsar