TPT-4431: Added support for SLADE and CLEO features

[ezilber-akamai]

📝 Description

Made root_pass optional for instance and instance disk creation (so long as at least one of authorized_users or authorized_keys is provided). Also added new boot_size and kernel fields to instance creation.

Also removed automatic root password generation to align with the fact that the field is now optional.

✔️ How to Test

make unit-test
make int-test

[Copilot]

Pull request overview

This PR updates the Linode Packer builder to support new instance/disk creation capabilities (notably optional root_pass when alternative auth is provided, plus new instance boot_size and kernel options), and temporarily points the plugin at a linodego fork that contains the required API surface.

Changes:

• Make root_pass optional for instance creation (and disk creation) when authorized_keys or authorized_users are provided.
• Add boot_size and kernel fields to instance creation and configuration decoding/docs.
• Update network interface flattening/tests to match updated linodego types (e.g., firewall_id pointer semantics).

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
go.mod	Adds a replace to a linodego fork to access new API fields/types.
go.sum	Updates module sums to reflect the linodego fork replacement.
builder/linode/config.go	Makes root_pass optional, adds validation rules, and introduces boot_size/kernel config fields.
builder/linode/config.hcl2spec.go	Adds HCL decoding support for boot_size, kernel, and disk-level root_pass.
builder/linode/step_create_linode.go	Sends root_pass as-is and adds boot_size/kernel to instance create options.
builder/linode/step_create_disk_config.go	Adds disk-level root_pass propagation and removes implicit password fallback behavior.
builder/linode/step_create_linode_test.go	Adjusts tests for updated firewall_id pointer shape.
builder/linode/config_test.go	Updates config prepare test inputs to satisfy new auth validation.
builder/linode/builder_test.go	Adds/updates tests covering root_pass optionality and boot_size/kernel behavior.
.web-docs/components/builder/linode/README.md	Documents boot_size/kernel and the updated auth requirements.

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