Doc: Add preseed filter examples

[roosterfish]

Fixes #1471.
Fixes #1301.

Creates a preseed reference page, references it and adds filter examples to how-to section.

cc @wideawakening

[Copilot]

Pull request overview

Adds a dedicated preseed reference page to the MicroCloud documentation, links it from the reference index, and updates how-to guides to point readers at the new reference while adding storage-disk filter examples.

Changes:

• Introduces /reference/preseed with a literalincluded preseed YAML and an explanation of disk filter syntax.
• Updates /reference/index to include the new preseed reference section.
• Adjusts initialization/joining how-tos to link to the full preseed reference and adds storage filter examples to initialization.

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
doc/reference/preseed.yaml	New reference YAML example used by the preseed docs (literalinclude).
doc/reference/preseed.md	New preseed reference page, including disk filter reference and constraints.
doc/reference/index.md	Adds a “Preseed” section linking to the new reference page.
doc/how-to/member_add.md	Replaces embedded YAML syntax block with a link to the new preseed reference.
doc/how-to/initialize.md	Replaces embedded YAML syntax block with a link and adds storage filter examples.

Suppressed comments (2)

doc/reference/preseed.md:65

• The current wording says string values "must not" be quoted, but the filter implementation supports quotes (and other docs/examples in this PR use quotes). Consider relaxing this to describe when quoting is required instead of forbidding it.

* Filters are checked in order of appearance
* String values must not be in quotes unless the string contains a space
* Single quotes are fine, but double quotes must be escaped

doc/how-to/initialize.md:259

• This snippet is intended to configure remote (Ceph) storage filters, but it uses storage.local instead of storage.ceph. That would make the example configure local storage filtering instead of Ceph.

storage:
  local:
    - find: size > 1TiB && model == "<vendor2>"
      find_min: 6
      find_max: 8

---

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[elijahgreenstein]

Nice! Some comments and suggestions about wording, organization, and the title and placement of the page on the Reference landing page.

[elijahgreenstein]

A few follow-up comments and suggestions.

[wideawakening]

great addition, thx!

maybe we can also add some 'debugging' tips, like using sudo microceph disk list --json or lxc query /1.0/resources | jq .

[roosterfish]

Thanks for your reviews @elijahgreenstein @wideawakening. I have addressed the remaining set of comments and added an additional note in the how-to mentioning the use of lxc query to find the actual filter values.

[elijahgreenstein]

LGTM