docs(release): add support Tiers and supported platforms per Tier

[gustavovalverde]

Motivation

As we get near to our Release Candidate, we should decide on which platforms we're going to support and the level of support and guarantees we'd like to ensure for each.

We've deploying with Debian in Docker and build with Ubuntu and MacOS in our CI, but we haven't defined an strategy around these platforms or how we're going to guarantee support, if any.

Fixes #4448

Solution

• Create a document including Tiers and the guarantees each "must" and "should" ensure for users and internally
• Create a document with the Supported Platforms (based from our actual build and test scenarios) linked to the respective Tier

This documents are based on Rust's approach with Tiers and Supported platforms https://github.com/rust-lang/rust/tree/master/src/doc/rustc/src

Review

Most people from @ZcashFoundation/zebra-team should have a look at this

Reviewer Checklist

• Verify correct wording is being used
• Teams and developer amounts relate to our reality
• Platforms and specific libraries relate to our reality
• Should we add information on why we dropped windows support?

Follow Up Work

• Add a resume to README.md targeting supported-platforms.md and target-tier-policies.md
• Create a PR including the release process based on these supported platforms

[teor2345]

This looks like a good start!

The target tier policy has a lot of rules that apply to the Rust compiler, but not Zebra. I'd suggest deleting those rules first, before making any other changes.

Zebra's project structure and processes are also different, so we'll need to update the remaining rules to match what we actually do. I added a comment the first time I saw each difference.

Since we copied these docs from the Rust project, can we credit them at the end of the doc?

[str4d]

We also recently set up platform support policies for zcashd based on the Rust ones, which you might find useful to look at for how we adapted them:

• https://zcash.github.io/zcash/user/platform-support.html
• https://zcash.github.io/zcash/dev/platform-tier-policy.html

[teor2345]

Thanks for the fixes, let me know when you want me to review this PR again.

[gustavovalverde]

@ZcashFoundation/general-rust-reviewers this is ready for general review.

@str4d thank you for sharing zcashd policies, it helped me improving the actual wording in some pieces.

[conradoplg]

Looks great!

I don't think we need to add an explanation about Windows, it's documented in tickets if someone wants to dig for information.

I won't approve for now so that others can take a look

[teor2345]

Looks good, thanks for all the updates!

I'll finish reviewing the detailed policy tomorrow.

[teor2345]

I finished my detailed review. It looks really good, I think it's pretty clear about what we want.

I noticed some Rust compiler-specific language, and some unclear or incorrect details.

My suggestions to fix them are in PR #4791.

[teor2345]

Thank you for all your work tracking down these details.

I made a bunch of final suggestions to resolve all outstanding comments.
Feel free to accept or reject them, I think we're getting to the final details now.

[teor2345]

Looks great, thanks!

Did you want to open a ticket to update the README and book indexes, or add it to the list of tasks in the release process ticket?

Things have changed a lot since our original release process draft. So the ticket and draft might be too complicated - we might want to delete the outdated parts before we start.

[gustavovalverde]

Did you want to open a ticket to update the README and book indexes, or add it to the list of tasks in the release process ticket?

Added it to the list of tasks in the release process ticket.