Add default index file for static directory

[terrywarwar]

*Issue #437

Default page index.html for static directory. localhost:3000 -> serves index.html

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[sanathkr]

Hey @terrywarwar Thanks for sending this PR! Actually, this feature is already supported. Checkout https://github.com/awslabs/aws-sam-cli#static-assets

This PR actually is not the solution for the issue #437. Root cause of this issue is different.

If the solution I gave you works, this PR won't be necessary. Let me know.

[terrywarwar]

Hi @sanathkr The static-assets work when I specify a page to load, but It doesn't serve the index.html by default for root path /, I get Missing Authentication Token

[sanathkr]

If you have an index.html at the root of the folder that is pointed by --static-dir, then it will serve index.html from there. You just need to adjust the folder to cover all the files you want.

I am not saying this is a perfect solution. SAM CLI's support for static websites can be improved. I created #523 for this purpose.

This Pull Request, unfortunately, is not accurate. sam local start-api is meant to start the Serverless backend (API+Lambda) but not really for the index.html or frontend resources. Untill #523 is solved, A better strategy would be to use a simple Node server or other tools start your web server to serve frontend resources, and use SAM CLI just for your backend.

In this light, this PR is not accurate. I am going to close this. Feel free to continue the discussion in #523.