Upgrade nginx ingress controller to 0.21 to support TLSv1.3

Seems no breaking change in 0.21

0.21 Changelogs:

• NGINX 1.15.6 with fixes for vulnerabilities in HTTP/2 (CVE-2018-16843, CVE-2018-16844)
• Support for TLSv1.3. Disabled by default. Use ssl-protocols ssl-protocols: TLSv1.3 TLSv1.2
• New annotation for canary deployments
• Support for configuration snippets when the authentication annotation is used
• Support for custom ModSecurity configuration
• LUA upstream configuration for TCP and UDP services .