Speed Improvements in the Playground

We rewrote most of Agenta's frontend. You'll see much faster speeds when you create prompts or use the playground.

We also made many improvements and fixed bugs:

• LLM-as-a-judge now uses double curly braces {{}} instead of single curly braces { and }. This matches how normal prompts work. Old LLM-as-a-judge prompts with single curly braces still work. We updated the LLM-as-a-judge playground to make editing prompts easier.
• You can now use an external Redis instance for caching by setting it as an environment variable
• Fixed the custom workflow quick start tutorial and examples
• Fixed SDK compatibility issues with Python 3.9
• Fixed default filtering in observability dashboard
• Fixed error handling in the evaluator playground
• Fixed the Tracing SDK to allow instrumenting streaming responses and overriding OTEL environment variables

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