docs: Improve log-viewer-webui dev docs.

[junhaoliao]

Request

To include:

1. That we have a npm script inside components/log-viewer-webui/package.json that can be directly used to start both the server and client.
2. CLP DB credentials should be configured before starting the debug server.
3. Instructions on installing deps for yscope-log-viewer.
4. That the statics assets inside yscope-log-viewer should be built before starting the log-viewer-webui server.

Possible implementation

See above request.