feat: support setting a plan

[oikarinen]

This pull request introduces support for managing Cloudflare plan types within the octodns_cloudflare provider. The change is implemented using a custom record type.

Aligned with change of _zones structure from #122

Key changes include:

• Added a new optional plan_type parameter to the CloudflareProvider class to specify the Cloudflare plan type (e.g., free, enterprise).
• Created a new custom record type CloudflareZoneRecord to support Cloudflare zone plan updates.
• Adjusted the _apply_Create, _apply_Update, and _apply_Delete methods to manage plan updates based on the new CF_ZONE record type.
• Updated README.md to document the new plan_type option.

[ross]

So played around with the option to add "meta" changes during the provider planning process in octodns/octodns#1236.

That should allow CloudflareProvider to implement _plan_meta and return a dictionary with information about the CF plan for the zone that can be used during the apply phase to make changes if necessary.

I believe all the code needed to get things to function is already in here, it'll just need to be shifted around a bit and the custom record type can go away.

LMK what you think and if you see any problems or shortcomings with the prototype implementation.

Once it's all vetted we can merge the octodns PR and then cut a release. This provider can then either bump to require that versuion of octoDNS or add support so that it makes the changes if octoDNS is new enough and warns or errors if someone is trying to manage the plan when it's not.

[oikarinen]

LMK what you think and if you see any problems or shortcomings with the prototype implementation.

Pretty straight forward and all good with this approach! Opened new PR and closing this

Once it's all vetted we can merge the octodns PR and then cut a release. This provider can then either bump to require that versuion of octoDNS or add support so that it makes the changes if octoDNS is new enough and warns or errors if someone is trying to manage the plan when it's not.

Code would support missing meta property but tests would require the change: #127