[PoC] feat: implement Contract tests for Fleet with Pact.io

[mdelapenya]

Summary

It basically adds Pact as a dependency and creates a Pact verifier for Fleet. It will fetch contracts from a Github URL (pushed here: elastic/e2e-testing#339).

How to test this locally

Firstly, we have to initialise Fleet using the UI, and for that we need to have ES and Kibana up and running.

$ yarn es snapshot --license trial -E xpack.security.authc.api_key.enabled=true

In another terminal:

yarn start --no-base-path

To run the contract tests:

$ cd x-pack
$ npm install
$ npm run test:pact --prefix plugins/ingest_manager

Other concerns

I was not able to bypass the pre-commit error about Pact needing to be added as a dependency to package.json, which I think it is already done.

[kibanamachine]

💔 Build Failed

• continuous-integration/kibana-ci/pull-request
• Commit: 2fbb1b3
• Pipeline Steps (look for red circles / failed steps)
• Interpreting CI Failures

Failed CI Steps

• Check Licenses
• Lint: eslint
• X-Pack Jest Unit Tests

Metrics [docs]

✅ unchanged

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[mdelapenya]

Things to do:

1. solve lint error for PactJS dependency:

error '@pact-foundation/pact' should be listed in the project's dependencies. Run 'npm i -S @pact-foundation/pact' to add it import/no-extraneous-dependencies

2. fix licenses for a third-party dependency:

ERROR Non-conforming licenses:
19:34:26 buffers
19:34:26 version: 0.1.1
19:34:26 all licenses: Custom: http://github.com/substack/node-bufferlist
19:34:26 invalid licenses: Custom: http://github.com/substack/node-bufferlist
19:34:26 path: ../../../kibana/node_modules/buffers

3. exclude Pact tests from Jest tests:

19:43:49 FAIL plugins/ingest_manager/fleet.pact.test.js
19:43:49 ● Test suite failed to run
19:43:49
19:43:49 TypeError: Request.defaults is not a function
19:43:49
19:43:49 5 | */
19:43:49 6 |
19:43:49 > 7 | const { Verifier } = require('@pact-foundation/pact');
19:43:49 | ^
19:43:49 8 |
19:43:49 9 | describe('Pact Verification', () => {
19:43:49 10 | it('validates the expectations of E2E Tests', () => {