Add separate SRCImage component exports to the package.json

[psd-coder]

There is known problem with package bundle size #98. This edit doesn't solve it, but allows importing SRCImage components using non-index file, like all other components and hooks, which allows avoiding having MUX player in your application bundle.

[netlify[bot]]

✅ Deploy Preview for react-datocms-example canceled.

Name	Link
🔨 Latest commit	3304dda68ddb885a96aba10e0a5a04a223a68e57
🔍 Latest deploy log	https://app.netlify.com/sites/react-datocms-example/deploys/67b4b480e1e3970008d7283d