Alpine: Update docker-base from 3.14 to 3.15

[adobejmong]

@bryanlatten / @ko-be / @bossjones : Update Alpine from 3.14 to 3.15. Alpine 3.15 released Nov 24, 2021 [1], [2]

Updated

• Update FROM version from 3.14 to 3.15 in Dockerfile-alpine

Notes to self:

A few things I picked from [2] that might impact some of the downstream images:

• New signing keys have been increased fro 2k to 4k. Make sure you have alpine-keys-2.4-r0 or later before upgrading to 3.15 (or downgrading from edge).
• nodejs LTS upgraded to version 16.13.0

[1] https://alpinelinux.org/posts/Alpine-3.15.0-released.html
[2] https://wiki.alpinelinux.org/wiki/Release_Notes_for_Alpine_3.15.0