proxy,ui-svelte: add request/response capturing (#508)

Add saving request and response headers and bodies that go through
llama-swap in memory.

- captureBuffer added to configuration. Captures are enabled by default.
- 5MB of memory is allocated for req/response captures in a ring buffer.
Setting captureBuffer to 0 will disable captures.
- UI elements to view captured data added to Activity page. Includes
some
QOL features like json formatting and recombining SSE chat streams
- capture saving is done at the byte level and has minimal impact on
llama-swap performance

Fixes #464 
Ref #503

config-schema.json

@@ -87,6 +87,12 @@
             "default": 1000,
             "description": "Maximum number of metrics to keep in memory. Controls how many metrics are stored before older ones are discarded."
         },
+        "captureBuffer": {
+            "type": "integer",
+            "minimum": 0,
+            "default": 5,
+            "description": "Size in megabytes of the buffer for storing request/response captures. Set to 0 to disable captures."
+        },
         "startPort": {
             "type": "integer",
             "default": 5800,