feat: set SENTRY_RELEASE env

[itsnotrisky]

I'm not sure if this is just my setup, but I found that new issues didn't get linked to any release created - it said Release: n/a in the sidebar.

Checking out the doc at Sentry.init({ release }) option I was wondering if this could be the reason - Sentry client didn't know where to link the issue. I scanned through the index.js file and didn't see anything is set for SENTRY_RELEASE.

I'm not aware if you can set env variable in Netlify through some API call, only thing I found is to set it through netlify.toml which means we need to update this file early before the build starts to insert some thing like SENTRY_RELEASE=process.env.COMMIT_REF CMIIW.

[jonesphillip]

@spondbob you are correct, in addition to using this build plugin you must also set the release in your SDK init. I've updated the readme to reflect this. There are a number of ways to access access the release in your SDK init. This is a good source of inspiration if you're still looking to do this (specifically the part with the setWebpackConfig):
https://cra.mr/instrumenting-gatsbyjs-with-sentry/

Closing this issue, but let me know if you have any other questions.