Add user meta to build environment

[chauncey-garrett]

Summary

It would be useful to include user meta in the build env vars so that meta can be passed on to an application's resources.

Motivation

By including user meta (e.g., the user who initiated a SYNC) as BUILD ENV vars, sync hooks for deployment annotations sent to an observability platform could provide further context around how a sync was initiated. It'd be important to distinguish between an auto sync'd application vs a manually synced one if this were provided.

Proposal

Something like ARGOCD_SYNC_USER_ID could be added to the existing set of build env vars (https://argo-cd.readthedocs.io/en/stable/user-guide/build-environment/).