[#5] feat(server): Add basic Jetty server support for Graviton

[jerryshao]

What changes were proposed in this pull request?

This PR proposes to add Jetty server support for Graviton.

Why are the changes needed?

The purpose of introducing Jetty as embedded web server is that:

1. Jetty is a light-weighted web server that can be easily embedded into our project compared to Tomcat and other services.
2. We basically don't want to introduce a bunch of Springboot related code to build our REST API. In that case, Jersey + Jetty would be the best choice.
3. If later on the performance of Jetty cannot meet our requirements, we can shift to use other web servers instead.

Fix: #5

Does this PR introduce any user-facing change?

N/A

How was this patch tested?

Local manual test

[xunliu]

LGTM