docs: add roadmap

[yizha1]

Description

What this PR does / why we need it:

Add roadmap which is missing in Ratify project.

Which issue(s) this PR fixes (optional, using fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when the PR gets merged):

This PR implemented one of the work items listed in issue #1334 for roadmap.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Helm Chart Change (any edit/addition/update that is necessary for changes merged to the main branch)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Please also list any relevant details for your test configuration

• Test A
• Test B

Checklist:

• Does the affected code have corresponding tests?
• Are the changes documented, not just with inline documentation, but also with conceptual documentation such as an overview of a new feature, or task-based documentation like a tutorial? Consider if this change should be announced on your project blog.
• Does this introduce breaking changes that would require an announcement or bumping the major version?
• Do all new files have appropriate license header?

Post Merge Requirements

• MAINTAINERS: manually trigger the "Publish Package" workflow after merging any PR that indicates Helm Chart Change

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Additional details and impacted files

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[sajayantony]

Can you link to some existing roadmaps which we can use as reference to review this?

[yizha1]

Can you link to some existing roadmaps which we can use as reference to review this?

Thanks @sajayantony

Here are some references from popular communities, which I checked while creating Ratify's roadmap. Not all the CNCF projects have the ROADMAP.md in their repository. Currently Ratify's roadmap is following the structure: First, the mission of Ratify project, then the strategy for the mission, and the roadmap in detailed steps and timeline from execution point of view.

• OPA Policy Roadmap in a slide format
• Fluxcd: https://fluxcd.io/roadmap/
• Harbor: https://github.com/goharbor/harbor/blob/main/ROADMAP.md
• Open telemetry: https://github.com/open-telemetry/community/blob/main/roadmap.md
• Jaeger: https://www.jaegertracing.io/roadmap/
• CRI-O: https://github.com/cri-o/cri-o/blob/main/roadmap.md
• Cilium: https://docs.cilium.io/en/latest/community/roadmap/

Please let me know if any further comments.

[akashsinghal]

Thanks for adding the roadmap. I would recommend @binbin-li @luisdlp @susanshi approve as well before merging.

[FeynmanZhou]

LGTM. I think it's ready for the first version and we could continuously update it by milestone.

[luisdlp]

Its a good first draft, some deliverable dates seem to aggressive or need to be scoped down.

[luisdlp]

This is not likely happening by September.

[yizha1]

Thanks @luisdlp. We can update this file in next iteration.

The base branch was changed.

[susanshi]

LGTM. thanks