feat: support streaming mode for push command

[justinkambic]

Depends on #575.

This patch will make it possible for the Synthetics Agent to push monitors to Kibana via a streams endpoint.

Testing this PR

Configure Kibana

Firstly, build and run the Kibana streaming PR. It is ok if it runs against a fresh local Elasticsearch cluster.

Once Kibana is running, log in as a user who can write (I simply used the elastic user), and create an API key, which we will supply to Synthetics for pushing.

Lastly, go to the Uptime application and enable monitor management. You should be prompted to create an Agent policy. Do this, following default options. Once your agent policy is created, the baseline configuration for Kibana is ready.

Configure Synthetics Project

0. Build synthetics: npm run build, npm link
1. Create a directory (can be a subdir in synthetics) mkdir beep, node dist/cli init beep, follow the prompt
2. Enter your new project: cd beep, npm link @elastic/synthetics
3. Perform a push: env SYNTHETICS_API_KEY={API_KEY} npm run push

Expected output

(node:92955) ExperimentalWarning: stream/web is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)
> preparing all monitors
> creating all monitors
> {MONITOR_NAME}: monitor updated successfully

[apmmachine]

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Build stats

• Start Time: 2022-08-17T15:35:53.423+0000

• Duration: 15 min 46 sec

Test stats 🧪

Test	Results
Failed	0
Passed	183
Skipped	2
Total	185

🤖 GitHub comments

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[dominiqueclarke]

This looks great to me!

Tested in 8.4.0 Kibana with streams, as well as in 8.3.0 Kibana without streams.

Tested creation, updates, and deletion.

Tested individual monitor errors (via failedMonitors), and the formatting for that is also working well.