✨Allow diskSetup to include partition layout

[miltalex]

What this PR does / why we need it:

This PR enhances disk partitioning capabilities by introducing support for custom partition layouts through the new DiskLayout field. Previously, disk partitioning was limited to a boolean option that could only create a single partition for the entire device. This enhancement allows users to define multiple partitions with specific size percentages and partition types.
The changes align with cloud_init logic's disk setup specification, which supports both boolean and list-based partition layouts. The existing layout boolean field is maintained for backward compatibility, while the new diskLayout field provides advanced partitioning capabilities when needed.

Examples

Before (Single Partition):

partitions:
  - device: /dev/sda
    layout: true  # Creates a single partition using entire disk

After (Multiple Partitions):

partitions:
  - device: /dev/sda
    diskLayout:
      - percentage: 33
      - percentage: 33
        partitionType: 82
      - percentage: 33

Generated cloud-init output:

disk_setup:
  /dev/sda:
    layout:
      - 33
      - [33, 82]
      - 33

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #8524

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: miltalex / name: Miltiadis Alexis (56bc6a0, 20133af, 3560524)

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[JoelSpeed]

Some initial thoughts on the API changes within this PR

[JoelSpeed]

You should include a required marker to show explicitly that this is required

[JoelSpeed]

What are the valid values for this value? And how would I, as an end user, understand those?

Is there a limit on this? Is 0 a valid value? Are negative values valid?

[miltalex]

Actually I can use a string here to reflect the correct linux partition types. It was an attempt to purely map the disk layout as described in the cloud init docs.

[JoelSpeed]

There's a choice to make here. Either you can allow all of the valid values there, in which case this should be a 2 character lowercase hex value. Or, you can allow specific, common types, and do that by creating an Enum here and creating PascalCase aliases to the formats we actually want to support.

IMO, the latter provides a better UX

[JoelSpeed]

I would avoid a type alias to a slice, it makes it harder to understand the API when looking at the go types (it looks like a struct for example if I look at the Partition usage)

[miltalex]

I will convert it to a struct

[JoelSpeed]

I just meant you could inline this slice, rather than using an alias, I don't think it needs to be a struct does it?

[JoelSpeed]

Godoc must start with the serialised version of the field name

Suggested change

	// Percentage of disk that partition will take (1-100)
	// percentage of disk that partition will take (1-100)

[JoelSpeed]

Suggested change

	// PartitionType is the numerical value of the partition type (optional)
	// partitionType is the numerical value of the partition type (optional)

[JoelSpeed]

Is this list ordered?

Can you validate that the percentages sum to 100? Are they allowed to sum to less than 100?