Disable npm configuration parameter engine-strict when installing dependencies of Jetpack

[fluiddot]

This PR disables the engine-strict parameter in Jetpack's .npmrc file as we can't ensure that the node version used by npm to check the engines parameter is the expected one. The parameter is reverted back after installing the dependencies.

NOTE: This change is a temporary workaround until we find a better solution to #5688.

To test:

1. Checkout the last commit from trunk branch of the Jetpack repository.
2. Run command npm install.
3. Observe that the command succeds.

Additionally, the fix has been also applied to #5687 in order to check that CI jobs succeed 🟢 .

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.

[SiobhyB]

@fluiddot, reviewed this, as well as the discussion on Slack, and confirmed npm install works perfectly with these changes applied. Thank you for getting to the bottom of this one 🙇‍♀️