[RUM-4060] Fix datadog-ci path resolving on iOS scripts

[marco-saia-datadog]

What does this PR do?

Introduces a better way to resolve the datadog-ci executable path, taking advantage of the node resolver.

Motivation

The iOS scripts added to the build phases by the Datadog Expo plugin depend on datadog-ci and they currently use a relative path, assuming that the cwd at execution time will always be the same, while it can actually vary depending on the setup.

Additional Notes

The core of the PR is:

if [[ -z "$DATADOG_CI_EXEC" ]]; then
    export DATADOG_CI_EXEC="$("$NODE_BINARY" --print "require('path').resolve(require('path').dirname(require.resolve('@datadog/datadog-ci/package.json')), '../../.bin/datadog-ci')")"
fi

This approach conforms to how Expo resolves paths, and it also allows to override DATADOG_CI_EXEC if ever needed.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests
• Make sure you discussed the feature or bugfix with the maintaining team in an Issue
• Make sure each commit and the PR mention the Issue number (cf the CONTRIBUTING doc)
• If this PR is auto-generated, please make sure also to manually update the code related to the change

[0xnm]

nice improvement!