[Workflow] Docs enhancements with stable release

[hhunter-ms]

Doc updates applicable to workflow going stable.

• [Workflow] JavaScript SDK support #3869
• [Workflow] Go SDK support #3868
• Add metrics documentation?
• Documentation for making workflow backend a configurable component Workflow backend documentation (workflow state store) #3924
• Python SDK decorators updates (Python SDK docs are outdated #4410)
• Remove 'beta' from code snippets and docs notes

[hhunter-ms]

related: #4366

[hhunter-ms]

Still need:

The notes in the Workflow docs about Workflow being in beta also need removed:

All the docs in Developing applications/Building blocks/Workflow section
The API reference doc

SDK docs and code snippets need updated as well, from each sdk repo:

.NET
Java
JS
Python