Prepare 0.8 release

[djc]

Proposed release notes

The 0.8 release contains substantial changes to make the API more modular. It integrates full support for ACME Renewal Information (ARI, recently standardized as RFC 9773).

• Add support for the ACME profiles extension draft (see Profiles #98).
• Add support for the ACME renewal information extension (see Implement ACME Renewal Information (ARI) #85).
• Add support for IP address identifiers (Add RFC 8738 IP address identifiers #97).
• Use a builder setup to build accounts via Account::builder() or Account::builder_with_http() (see Use builder pattern for Account creation #110).
• NewOrder values must be created through a builder as well (via NewOrder::new()).
• Authorizations can now be accessed via a stream-like API available through Order::authorizations() (see Scope API to wrapper types #92).
• Integrated API to poll order readiness and certificate, with configurable retry policy (see Encapsulate retry policy in a type #108, poll certificate function #121).

When upgrading, consider reviewing the diff for our example code.

[cpu]

Changes in this branch LGTM.

For the release notes, here are some other items I noticed that feel worth mentioning:

• Add support for ACME subproblems (#81)
• Add support for ACME account and authorization deactivation (#89)
• Add support for ACME account key rollover and contact information update (#100)
• Add support for ACME device attestation draft (experimental) (#126)

There were a few other small things I noticed reviewing the diff since last release, but they don't feel like headline items (e.g. the account thumbprint thing, loading account from an existing key, etc).

[cpu]

Project MSRV increased to 1.70

I was wrong here. I thought we updated to 1.71, but looked and the MSRV is 1.70. That change was made in the previous release (https://github.com/djc/instant-acme/releases/tag/0.7.2) so there's nothing to mention here. Deleted from my initial comment.