Deprecate Rhino JavaScript engine

[bartekpacia]

TL;DR

We will deprecate Rhino JavaScript engine, thus making GraalJS the only choice.

To prepare for this, explicitly set jsEngine: graaljs in front-matter of every flow that uses JavaScript:

appId: com.example.app
jsEngine: graaljs # <-- Opt-in to use GraalJS engine
---
- launchApp
- runScript: ./myScript.js

Plan

Let's do it in phases, to spare our users sudden breakages.

Phase 1 - communicate

• Communicate to community our intent to deprecate RhinoJS
  • [ ] In our public Slack workspace, in the #announcements channel
  • [ ] In v1.39.0 release Medium post
  • [ ] In v1.39.0 CHANGELOG.md
  • [ ] In our JavaScript docs

Phase 2 - soft warning

• [ ] Add warning (in both CLI and Maestro Cloud) if GraalJS is not used to execute a flow (i.e. jsEngine: graaljs is not set, or MAESTRO_USE_GRAALJS env var is not set).
• [ ] Ping the community once again about our intent to deprecate GraalJS

Phase 3 - change default

• [ ] Change default JS engine to GraalJS (in both CLI and Maestro Cloud)
• [ ] Display warning if RhinoJS is used (with jsEngine: rhinojs)

Phase 4 - remove RhinoJS

• [ ] Remove RhinoJS completely from Maestro codebase
• [ ] Display warning if jsEngine or MAESTRO_USE_GRAALJS are set - say that "these config options don't have any effect anymore"

Notes

• GraalJS was implemented in PR #1147
• As we move ahead with phases, we will listen for user feedback and help them migrate to GraalJS, by fixing possible bugs in Maestro when GraalJS is used and improving docs.