add license checker to web-console

[clintropolis]

This PR modifies druid-console to add a 'dev dependency' to a lib called license-checker and adds a check-licenses npm "script" that is run by maven to ensure dependencies are apache license compatible. A file containing all licenses, web-console/licenses.json, is also generate during build for usage with license collection stuff in #7026.

Output during maven execution:

...
[INFO] --- frontend-maven-plugin:1.6:npm (license-check) @ druid-console ---
[INFO] Running 'npm run check-licenses' in /Users/clint/workspace/clintropolis/druid/web-console/target
[INFO] 
[INFO] > web-console@0.14.0 check-licenses /Users/clint/workspace/clintropolis/druid/web-console
[INFO] > license-checker --production --onlyAllow 'Apache-1.1;Apache-2.0;BSD-2-Clause;BSD-3-Clause;MIT;CC0-1.0' --summary
[INFO] 
[INFO] ├─ MIT: 74
[INFO] ├─ BSD-3-Clause: 4
[INFO] ├─ Apache-2.0: 3
[INFO] └─ (GPL-2.0 OR MIT): 1
[INFO] 
[INFO] 
...