Update the alpine image in Pravega Operator to 3.15

[nishant-yt]

Description

The latest pravega-operator image has OpenSSL 1.1.1l installed which contains CVE-2021-4160 . This has been fixed in OpenSSL 1.1.1m+ versions. Though the alpine:3.14 has OpenSSL 1.1.1n , it seems the latest pravega-operator image does not contains that fix. So it's recommended to update the alpine image from 3.14 --> 3.15

Importance

must-have

Location

https://github.com/pravega/pravega-operator/blob/master/Dockerfile

Suggestions for an improvement

Update the alpine image version to 3.15