Configure CORS for the batching server

[ebma]

Context

The batching server currently does not configure CORS and by default, all requests from a browser are disabled. We want to enable CORS in order to be able to query prices from the portal frontend.

This is needed for https://github.com/pendulum-chain/portal/issues/439.

TODO

• Add actix_cors middleware to the batching server.
• Configure it so that it can be used to query data from the /currencies POST endpoint.
• It should at least allow the origin portal.pendulumchain.org. We can also think about enabling netlify deployments in the CORS settings.

[ebma]

@pendulum-chain/product this is blocking https://github.com/pendulum-chain/portal/issues/439 and in order to unblock it we should work on this very soon.

[prayagd]

Hey team! Please add your planning poker estimate with Zenhub @b-yap @bogdanS98 @ebma @gianfra-t @TorstenStueber