Document inst.script (bsc#1246702, gh#agama-project/agama#2589)

Author: mvidner

docs/user/unattended/autoyast/index.md

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 # AutoYaST support

docs/user/unattended/inst-script.md

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+sidebar_position: 4
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+
+# Fully scripted installation
+
+In some cases even Jsonnet evaluation may not be enough to fully support complex installation decision making.
+
+To replace the regular installation process, use the
+`inst.script` [boot option](../boot_options). You can use any of the
+[URLs that Agama supports](../urls). It can be used repeatedly.
+
+It downloads a file, makes it executable and runs it. It is suggested to run these
+commands as part of the script:
+- `agama config load`
+- `agama install`
+
+If `inst.auto` is also present, it is processed after `inst.script`.
+
+:::warning Experimental feature
+
+With [`inst.auto`](working-with-profiles) we commit to backward compatibility, but
+with `inst.script`, as it is a last minute feature, we reserve the freedom to evolve
+Agama even in ways that may break this year's `inst.script` programs.
+
+We plan to specify this feature better and stabilize it by SP1, the first service pack.
+
+:::
+
+:::note In-profile scripts
+
+For scripts more limited in scope, specified as part of the JSON profile, see the [Running scripts](profile/scripts).
+
+:::

docs/user/unattended/profile/scripts.md

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 This section describes how to specify a script and goes through some use-cases.
 
+:::note `inst.script`
+
+For a more general script feature wrapping the whole installation process, see [Fully scripted installation](../../inst-script)
+
+:::
+
 ## Scripts definition
 
 User scripts are defined in the `scripts` section of the Agama profile. There is a key for each of