Remove tomcat-embed-websocket exclusion

[sdeleuze]

With #178, we now leverage Tomcat 9.0.6 which allows us to remove tomcat-embed-websocket exclusion.

@fhanik Notice as expected this change has an impact on the footprint:

With tomcat-embed-websocket exclusion:

Build memory: 5.72GB
Image build time: 104.1s
RSS memory: 86.8M
Image size: 67.6M

Without tomcat-embed-websocket exclusion:

Build memory: 5.91GB
Image build time: 103.5s
RSS memory: 88.4M
Image size: 68.5M