upgrade alpine base image to v3.15.0 including upgrade of dovecot package to v2.3.17-r2 and socat package (see below)
https://web.archive.org/web/20211204115525/https://dovecot.org/doc/NEWS
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=0678b7b851f0d339a972e97b7105e3a1eac45667
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=f3d3b2d920bafb894bdc14abfcc3b381685c8615
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=48ca8f9a0a64fb573c628a9dd2ecf226005e1821
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=4277294f32337ed0f8cfa166d9691dc1ad2f9ba1
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=701fc860230ab0d1bb80fcf51183100312566045
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=2cf3fe063b1b9e308372af7e2c2348e9e494a135
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=2ea836554c060b727628e2852e8094852e4ff7fe
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=57e2797a08b2d2713484098598d3ee07b785642c
https://git.alpinelinux.org/aports/commit/main/dovecot?h=3.15-stable&id=50d6ff73e7ab1d4eccb5327cf15fed51fa092aeb
https://web.archive.org/web/20211204114944/https://fossies.org/linux/socat/CHANGES
https://git.alpinelinux.org/aports/commit/main/socat?h=3.15-stable&id=f3d3b2d920bafb894bdc14abfcc3b381685c8615
https://git.alpinelinux.org/aports/commit/main/socat?h=3.15-stable&id=670bf5a8cc5bc605eede8ca2fd55b50a5c9f8660
https://git.alpinelinux.org/aports/commit/main/socat?h=3.15-stable&id=c27210ca4e207b19b419eccaaa53fa33d3ee3efe