Introduce retry mechanism for npm install in CI/CD

This commit addresses occasional pipeline failures caused by transient
network errors during dependency installation with `npm ci`. It
centralizes the logic for installing npm dependencies and introduces a
retry mechanism.

The new approach will attempt `npm ci` up to 5 times with a 5-second
interval between each attempt, thereby increasing the resilience of
CI/CD pipelines.

This commit adds a new script `npm-install.js` with `npm run
install-deps` command to centralize npm dependency installation process
throughout the project. Separate testing of scripts to a separate
workflow.

It removes unused `install` dependency from `package.json`.

README.md

@@ -76,6 +76,12 @@
       src="https://github.com/undergroundwires/privacy.sexy/workflows/checks.desktop-runtime-errors/badge.svg"
     />
   </a>
+  <a href="https://github.com/undergroundwires/privacy.sexy/actions/workflows/checks.scripts.yaml" target="_blank" rel="noopener noreferrer">
+    <img
+      alt="Status of script checks"
+      src="https://github.com/undergroundwires/privacy.sexy/workflows/checks.scripts/badge.svg"
+    />
+  </a>
   <a href="https://github.com/undergroundwires/privacy.sexy/actions/workflows/checks.external-urls.yaml" target="_blank" rel="noopener noreferrer">
     <img
       alt="Status of external URL checks"