Add environment variables to sample-apps

[vferraro-scottlogic]

Background

We have a vite.config.js file in showcase/ which sets some environment variables. The "Local" env variable is used inside useLayoutManager hook to determine whether to use the local or remote persistence manager. We want the same environment variable to be available in sample-apps/

Work Required

• make environment variable "local" available within vuu-ui/sample-apps. Should be accessible through global process (i.e. process.env.LOCAL) (vite.config.js? .env?)
• add entry for process.env.LOCAL in main build (esbuild.mjs) i.e. see showcase vite.config.js and main build script
• add flag location to layout server documentation
• remove check on process.env.LOCAL in useLayoutManager

[cfisher-scottlogic]

Updated documentation here.