docs: update buildgc example config to use new buildkit v0.17 options

[dvdksn]

Signed-off-by: David Karlsson 35727626+dvdksn@users.noreply.github.com

- What I did

Updated the example builder gc config in the dockerd reference to use the new
options introduced in buildkit v0.17.

- How I did it

Tested manually

A couple small inconsistencies I noticed when doing this:

• The filter field in daemon.json uses a single = to assign filters, whereas builder uses ==, for example: type==source.git.checkout
• The size values in daemon.json are human-readable bytes. But BuildKit also allows percentage values. Attempting to set eg "minFreeSpace": "20%" results in config parse error.

- A picture of a cute animal (not mandatory but encouraged)

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[thaJeztah]

Perhaps @crazy-max or @jsternberg can help review 😅

These options always confuse me (e.g. in this case maxUsedSpace being 512MB, but other options having a larger size).

The filter field in daemon.json uses a single = to assign filters, whereas builder uses ==, for example: type==source.git.checkout

Is that something that should be aligned? I also recall the "single filter allowed" part on the daemon, and was confused by that (i.e., the daemon disallows multiple filters, but I couldn't find why it added that restriction); moby/moby#46864

[dvdksn]

I think alignment would be great. I see no reason that the formats should be separate. Also for the size values.

[crazy-max]

Was looking at related PR on moby moby/moby#48720 and your changes look good to me.

We should also update https://docs.docker.com/build/cache/garbage-collection/#docker-daemon-configuration-file and on this page we show filters with == in some cases:

{
  "builder": {
    "gc": {
      "enabled": true,
      "policy": [
        {
          "keepStorage": "2.764GB",
          "filter": [
            "unused-for=48h",
            "type==source.local,type==exec.cachemount,type==source.git.checkout"
          ]
        },
        { "keepStorage": "20GB", "filter": ["unused-for=1440h"] },
        { "keepStorage": "20GB" },
        { "keepStorage": "20GB", "all": true }
      ]
    }
  }
}

I recall I made some changes in our buildx docs for the available filters: docker/buildx#3392. We define the operators = for equality, != for not equal and ~= for a regular expression.

[dvdksn]

Yeah I will update there to use the new properties and correct delimiter as well 👍🏻

[dvdksn]

Really nice filter addition to the docs btw ❤️