providers: Add "akamai" provider

[nesv]

The "akamai" provider adds support for retrieving configuration from Akamai Connected Cloud's (a.k.a. Linode) Metadata Service.

References: flatcar/Flatcar#1404
References: coreos/fedora-coreos-tracker#1701
References: coreos/ignition#1841

Note

I'll push any requested changes as fixup commits, just so that the Github comment threads don't get messed up. If this PR is approved, I will squash these fixup commits out prior to merge.

[prestist]

@nesv Awesome, thank you for doing this!

Took a quick look at it, and overall it looks sane, I need to do some double checking on some of the meat of the mod.rs but so far so good!

[nesv]

@nesv Awesome, thank you for doing this!

Took a quick look at it, and overall it looks sane, I need to do some double checking on some of the meat of the mod.rs but so far so good!

Thanks a bunch, @prestist!

I misunderstood how serde handles deserializing untagged enums. I had hoped I could use an enum to enumerate all possible values for a field, but it would seem that isn't possible; I have removed the InterfacePurpose enum, in favour of an Option<String>, but I am not too enthused with that tradeoff. It feels like a loss in precision, though it does keep things flexible should the API change in the future.

[nesv]

I was hoping to provide an as-complete-as-possible MetadataProvider implementation, but I don't think there is enough networking information that comes from Linode's Metadata Service to be able to implement the MetadataProvider::networks method.

[nesv]

The latest patches have been checked, and they work! All of the fixup commits have been squashed and rebased onto main.

[tormath1]

FWIW, same as the Ignition PR (coreos/ignition#1841) it has been tested on Flatcar and it works as expected on Akamai/Linode from a functional aspect.

[nesv]

@jlebon Requested changes have been made! Thank you for taking the time to review this PR.

[jlebon]

LGTM overall, though looks like there are a few lints to address. While we're here, can you squash your fixup commits together? We don't "Squash and merge" in this repo.

[nesv]

LGTM overall, though looks like there are a few lints to address.

Gah, oversights on my part. I'll get those fixed up.

While we're here, can you squash your fixup commits together? We don't "Squash and merge" in this repo.

Absolutely! I was planning on squashing my own fixup commits out anyways. 😄

[nesv]

@jlebon Fixup commits squashed, and I've applied the linting suggestions.