Add support for a custom Agent

[dhoko]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Feature, we add support for a custom Agent when we create requests via ws or fetch. cf https://nodejs.org/api/http.html#http_new_agent_options

• What is the current behavior?

If you have a proxy set ex: inside a CI, Node.JS will break cf nodejs/node#15620 so you need to be able to use a custom agent.

• What is the new behavior (if this is a feature change)?

It works :)

• Other information:

[dhoko]

I didn't fix the test from │./tests/analysis.spec.ts because it's random. If I copy/paste the output from corrected the corrected version will change etc. etc. I don't understand.
Ex:

Run 1

 FAIL  tests/analysis.spec.ts                                                                                
  ● Console                                                                                                  
                                                                                                             
    console.log tests/analysis.spec.ts:16                                                                    
      When we have shuffled off this mortal coil,                                                            
        Must give us pause - tthere'sthe respect                                                             
        That makes calamity of so long life.                                                                 
                                                                                                             
  ● further analysis of results › corrects a result                                                          
                                                                                                             
    expect(received).toEqual(expected) // deep equality                                                      
                                                                                                             
    - Expected                                                                                               
    + Received                                                                                               
                                                                                                             
      When we have shuffled off this mortal coil,                                                            
    -   Must give us pause - their's the respect                                                             
    +   Must give us pause - tthere'sthe respect                                                             
        That makes calamity of so long life.                                                                 

Run 2

 FAIL  tests/analysis.spec.ts                                                                                 
 ● Console                                                                                                   
                                                                                                             
   console.log tests/analysis.spec.ts:16                                                                     
     When we have shuffled off this mortal coil,                                                             
       Must ggiveus pause - tthere'sthe respect                                                              
       That makes calamity of so long life.                                                                  
                                                                                                             
 ● further analysis of results › corrects a result                                                           
                                                                                                             
   expect(received).toEqual(expected) // deep equality                                                       
                                                                                                             
   - Expected                                                                                                
   + Received                                                                                                
                                                                                                             
     When we have shuffled off this mortal coil,                                                             
   -   Must give us pause - tthere'sthe respect                                                              
   +   Must ggiveus pause - tthere'sthe respect                                                              
       That makes calamity of so long life.