Deploy app on Elastic Beanstalk

[stulacy]

Currently the app is hosted in Lightsail, but Elastic Beanstalk offers several advantages:

• Price is the main benefit, with a Lightsail container instance running with 1vCPU and 2GB RAM costing $40 vs $6.6 in EB (2vCPU but 1GB RAM)
• EB makes it easy to have a separate Dev and Prod environment without needing to keep two entirely separate stacks with different container images
• There's no need to store images in ECR as EB builds from docker-compose files during deployment
• EB is a bare wrapper around EC2, so we can access the underlying EC2 instance if needed and it's easier to integrate with other AWS products, such as ACM
• EB is fully describable within CloudFormation unlike Lightsail, so this PR closes #133 & #134

Outstanding tasks:

• [ ] Decide on the production environment specs
• [ ] Sort SSL - might only be able to request the certificate in CloudFormation and will need to manually validate it and add to the instance. ACM certs can only be added to CloudFront or load balancers, I think the former would be more appropriate here, not least to help #202
• [ ] Refactor the Deploy script. Currently there's 2 separate actions for dev and prod with nearly identical steps, the only difference being how the version string is generated. I imagine this is the type of thing that can be done with GitHub Environments

[stulacy]

I haven't been able to get the SSL from CloudFront working yet for several reasons:

• CloudFront doesn't natively support EBS apps
• CloudFront can work with any custom URL, but EBS doesn't export URLs as CloudFormation resources, so you'd need to add a Lambda custom resource to get the URL
• Furthermore, even when manually creating a CloudFront distribution in the AWS Console and passing it an EBS URL, it still doesn't work out of the box (returns 504)

Instead, there seem to be 2 solutions:

1. Give up and use a load balancer which supports certificates directly from ACM. Estimate ~$20 per month so still half of what LightSail costs, but still an unnecessary resource for a low-traffic app
2. Get an SSL cert manually and embed it directly into the app and configuring nginx to use it. Costs more developer time, need to keep cert out of repo etc...

Any thoughts @kilicomu ? I'm leaning towards the former as I'm not keen on spending much more time on this, although if you have any advice about how to sensitively bundle the SSL cert with the app for distribution then it might be worth exploring the second route

[stulacy]

Closing because App Runner has been identified as a more suitable deployment location