Change react to a peer dependency for a11y-addon

[jmakGH]

Is your feature request related to a problem? Please describe.
The a11y-addon has react as a normal dependency at ^16.8.3 which leads to incompatibility issues for us as a consumer since we're using a pinned version of react@16.9.0. This is due to Storybook bundling the latest minor version of react, which is 16.12, resulting in there being two versions of React being used within the same tree which causes the following error to be thrown:

Describe the solution you'd like
Is it possible to change react to being a peerDependency: * such as how the centered or knobs addons specify it? This keeps inline with the premise that Storybook/react functions independent of whatever version of React a consumer is using.

Describe alternatives you've considered
At this point, we can only drop the addon or implement our own version.

Are you able to assist bring the feature to reality?
Yes I can

[shilman]

@jmakGH sounds totally reasonable. PR welcome! perfect time for it too, since we're on 6.0 and this is probably (technically) a breaking change.

[jmakGH]

Thank you, PR submitted!

[stale]

Hi everyone! Seems like there hasn't been much going on in this issue lately. If there are still questions, comments, or bugs, please feel free to continue the discussion. Unfortunately, we don't have time to get to every issue. We are always open to contributions so please send us a pull request if you would like to help. Inactive issues will be closed after 30 days. Thanks!

[jmakGH]

Resolved by #9957

[shilman]

ZOMG!! I just released https://github.com/storybookjs/storybook/releases/tag/v6.0.0-alpha.28 containing PR #9957 that references this issue. Upgrade today to try it out!

You can find this prerelease on the @next NPM tag.