s/npm install/npm ci/ in tests and builds

[trentm]

We should use npm ci where ever we are using npm install in our CI and tests:

% rg 'npm install' .ci test dev-utils
dev-utils/make-lambda-layer-zip.sh
36:npm install --global-style elastic-apm-node-*.tgz

test/script/docker/run_tests.sh
39:      npm install

.ci/Jenkinsfile
541:                bat 'npm install'

.ci/scripts/docker-test.sh
34:  until npm install; do
39:      printf "Retry of 'npm install' %s/%s exited %s, retrying in %s seconds...\n" "$count" "$retries" "$exit" "$wait" >&2

.ci/scripts/test_basic.sh
5:npm install

.ci/scripts/test_types_babel_esm.sh
5:npm install

.ci/scripts/prepare-benchmarks-env.sh
4:# to use this) and `npm install`.
29:npm install

.ci/Makefile
12:		npm install --global-style https://github.com/elastic/apm-agent-nodejs#$(BRANCH_NAME); \

Note that we can only do this with npm v6 and later, which means we have to wait until we drop node v8 support.

• [ ] Does npm ci support --global-style used for the lambda layer and docker container?