[FE-2750][FE-2754] Support connection pool and network level timeouts and maxConns in ClientConfiguration

[cleve-fauna]

Ticket(s): FE-2750, FE-2754

Problem

1. Need to support connection pooling.
2. Need to support network level timeouts.
3. Need a way to run integ tests

Solution

1. Utilize agent-keep-alive to build a connection pool and enforce network level timeouts. Agent-keep-alive fixes an outstanding bug in NodeJS's underlying HTTP Agent where IP changes on the server are not well handled. See here.
2. Set timeout for network issues.
3. Reconfigured the tests to optionally run as integ tests against a "real" endpoint.

Result

Client pool settings and such available to the user.

Out of scope

Vending a default client configuration.

Testing

Tested locally:

~/workplace/fql-x-javascript (main_sp_wp_clientConfig) » yarn test                                                                                                                                                                                                                                                                                                      
 $ jest
 PASS  __tests__/functional/client-configuration.test.ts
 PASS  __tests__/integration/query.test.ts

Test Suites: 2 passed, 2 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        2.663 s
Ran all test suites.
 ✨  Done in 3.90s.

and against preview:

~/workplace/fql-x-javascript (main_sp_wp_clientConfig) » endpoint="https://db.prev.faunadb.net" secret=REDACTED yarn test                                                                                                                                                                                                                cleve@Cleves-MBP
 $ jest
 PASS  __tests__/functional/client-configuration.test.ts
 PASS  __tests__/integration/query.test.ts

Test Suites: 2 passed, 2 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        2.558 s, estimated 3 s
Ran all test suites.
 ✨  Done in 3.10s.

[cleve-fauna]

Please do not merge until #1 and #2 are merged.

[freels]

LGTM, though I think it would make sense to ask for at least on DX person to take a look at these, since with the exception of Jake, I'm not sure we can give you as valuable feedback on the JS aspect of the code.