feat(dev): add command to update composer deps

[bshaffer]

Command to set or bump composer deps.

This will be useful for implementing a GitHub Action to run the google/cloud package tests against new versions of GAX and Auth libraries before release.

TODO

• add tests for the new command
• consider using this command to replace logic done in: (this became overly complicated)

  google-cloud-php/.github/run-package-tests.sh

  Lines 32 to 38 in 43b4687

  	for i in BigQuery,cloud-bigquery Core,cloud-core Logging,cloud-logging PubSub,cloud-pubsub Storage,cloud-storage ShoppingCommonProtos,shopping-common-protos,0.1; do
  	IFS=","; set -- $i;
  	if grep -q "\"google/$2\":" ${DIR}/composer.json; then
  	if [ -z "$3" ]; then VERSION="1.100"; else VERSION=$3; fi
  	composer config repositories.$2 "{\"type\": \"path\", \"url\": \"../$1\", \"options\":{\"versions\":{\"google/$2\":\"$VERSION\"}}}" -d ${DIR}
  	fi
  	done

[vishwarajanand]

unrelated to this PR, but should this not be exit instead?

[bshaffer]

no, because we want to run all the tests even if one fails, so we can see if the others succeed or not. By sending the error in FAILED_FILE, we ensure that we will exit below.

[vishwarajanand]

Lgtm, left a few nits