Move Alpine floating tags from 3.20 to 3.21

[lbussell]

Fixes #6178

I made this edit using regexes and documented it for future reference. Expand the details to see the patterns that were used.

How to replace Alpine floating tags with regex

First, match all Alpine tags.

( )*("\$\((?:dotnet|sdk)\|\d+\.0\|minor-tag\))(-alpine)((?:3.\d+)?)((?:-aot)?(?:-extra)?(?:-composite)?(?:-(?:amd64|arm64v8|arm32v7))?")(: \{\})

We can modify this to select floating tags only. I chose to match two lines in order to get the previous line which will need to be modified since it has a comma.

Regex capture groups:
 1   2                                         3         4           5
(\s+)("\$\((?:dotnet|sdk)\|\d+\.0\|minor-tag\))(-alpine)((?:3.\d+)?)((?:-aot)?(?:-extra)?(?:-composite)?(?:-(?:amd64|arm64v8|arm32v7))?"): \{\}(?:,)?\n\1\2\3\5\{6}: \{\}

Remove all Alpine floating tags

(\s+)("\$\((?:dotnet|sdk)\|\d+\.0\|minor-tag\))(-alpine)((?:3.\d+)?)((?:-aot)?(?:-extra)?(?:-composite)?(?:-(?:amd64|arm64v8|arm32v7))?"): \{\}(?:,)?\n\1\2\3\5: \{\}

Replace with

$1$2$3$4$5: {}

Add new floating tags to precise Alpine version

In this example we want to add floating tags to Alpine 3.21. For each image, Find the last Alpine 3.21 tag without a floating tag (it won't have a comma at the end of the line).

                                      Change the number -----,
                                                             V
(\s+)("\$\((?:dotnet|sdk)\|\d+\.0\|minor-tag\))(-alpine)((?:3.21)?)((?:-aot)?(?:-extra)?(?:-composite)?(?:-(?:amd64|arm64v8|arm32v7))?"): \{\}

Replace with the following to add the floating tags back.

$1$2$3$4$5: {},\n$1$2$3$5: {}