templates: add linuxbrew

This template does not use macOS as the guest OS, because it seems hard to automate
provisioning macOS instances (accept EULA, skip enabling iCloud, set up SSH...).

To run Homebrew on macOS with a sandbox, Alcoholless can be used instead.
The `alclessctl` CLI of Alcoholless is desigined to be similar to `limactl`:
https://github.com/AkihiroSuda/alcless

```
alclessctl create default
cd ~/SOME_DIRECTORY
alcless brew install xz
alcless xz SOME_FILE
```

Signed-off-by: Akihiro Suda <[email protected]>

Author: AkihiroSuda

templates/README.md

@@ -33,6 +33,9 @@ Distro:
 - [`experimental/opensuse-tumbleweed`](./experimental/opensuse-tumbleweed.yaml): [experimental] openSUSE Tumbleweed
 - [`experimental/debian-sid`](./experimental/debian-sid.yaml): [experimental] Debian Sid
 
+Alternative package managers:
+- [`linuxbrew.yaml`](./linuxbrew.yaml): [Homebrew](https://brew.sh) on Linux (Ubuntu)
+
 Container engines:
 - [`apptainer`](./apptainer.yaml): Apptainer
 - [`apptainer-rootful`](./apptainer-rootful.yaml): Apptainer (rootful)

templates/linuxbrew.yaml

@@ -0,0 +1,40 @@
+# Homebrew on Linux.
+#
+# Useful for sandboxing `brew` in an isolated environment.
+#
+# This template does not use macOS as the guest OS, because it seems hard to automate
+# provisioning macOS instances (accept EULA, skip enabling iCloud, set up SSH...).
+
+minimumLimaVersion: 1.1.0
+
+base:
+- template://_images/ubuntu-lts
+# Remove this line to disable the mounts
+- template://_default/mounts
+
+# containerd should be installed via Homebrew when Homebrew supports it
+containerd:
+  system: false
+  user: false
+
+provision:
+- mode: data
+  path: /etc/profile.d/99-linuxbrew.sh
+  # nofile is increased due to https://github.com/Homebrew/brew/issues/9120
+  content: |
+    ulimit -n 65536
+    [ -e /home/linuxbrew/.linuxbrew/bin/brew ] && eval "$(/home/linuxbrew/.linuxbrew/bin/brew shellenv)"
+- mode: system
+  script: |
+    #!/bin/bash
+    set -eux -o pipefail
+    command -v gcc >/dev/null 2>&1 && exit 0
+    export DEBIAN_FRONTEND=noninteractive
+    apt-get update
+    apt-get install -y build-essential
+- mode: user
+  script: |
+    #!/bin/bash
+    set -eux -o pipefail
+    [ -e /home/linuxbrew ] && exit 0
+    /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"