Epic: Implement Context values for Segments

[khvn26]

Closes #136.
Closes #5557.
Closes #5635.

DoD

In addition to Trait keys, two kinds of Context values are supported in Core API, Edge API, and Edge Proxy:

1. Environment Name
2. Identifier

All segment operators, including % Split, are unlocked for usage against Environment Name, Identifier, and Traits.

Segment flyout UI is updated so Context values are accepted in addition to Traits.

Notes

Preliminary/research work:

• UX/docs: docs: Context values for Segments #5654
• Engine: feat: Add segment types, segment metadata, identity override segments support flagsmith-engine#198