Rebase to baseimage-alpine v3.19

[seanD111]

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• I have read the contributing guideline and understand that I have made the correct modifications

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Description:

Changed baseimage-alpine:3.18 to baseimage-alpine:3.19 in Dockerfiles

Benefits of this PR and context:

Rebasing to alpine 3.19 makes this image more consistent with others (i.e., swag) especially when it comes to packages pulled from the alpine apk community index http://dl-cdn.alpinelinux.org/alpine/v{version}/community/x86_64/APKINDEX.tar.gz

How Has This Been Tested?

I cloned this fork and used it to build a service in a docker-compose file:

services:
  borg-server:
    build: ./docker-openssh-server

With version 3.18, borgmatic-1.7.14-r0.apk would be pulled from the alpine apk community index. With version 3.19, borgmatic-1.8.8-r0.apk would be pulled, which has different syntaxes. After building with 3.19 via compose, borgmatic works consistently with other LinuxServer images that have been rebased to 3.19

Source / References:

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[aptalca]

Thanks for the PR, but the rebase for this image requires changes to the Jenkinsfile, which require a team member to open a PR from another repo branch for proper test builds.

We're handling it here: #84