Optimize url encoding, use default port for debugger service

[annagrin]

• Optimize encoding of the extension url by not awaiting on the result until needed.
  • This cuts the startup time of dwds.
• Try binding debug service to a constant port if possible.
  • This will help with caching VM's API responses.

closes: #1400
helps: #1401

[annagrin]

I will wait with submitting this until we have metrics ready.

[annagrin]

rebased onto latest master