Add SSE fallback to some one way WS connections

[EhabY]

Add SSE fallback to some WS connections:

• /api/v2/workspaces/${workspace.id}/watch-ws -> /api/v2/workspaceagents/${agentId}/watch-metadata
• /api/v2/workspaceagents/${agentId}/watch-metadata-ws -> /api/v2/workspaceagents/${agentId}/watch-metadata

Restored the previous code regarding createStreamingFetchAdapter to stream in SSE events.

• Implemented a unified interface for WS and SSE to be similar to the OneWayWebSocket.
• Added unified logging for WS and SSE.
• Fixed issue with headers order precedence
• Add tests for CoderApi

Closes #620

[mtojek]

I haven't looked into tests yet, but I can give a few observations now 👍

[mtojek]

LGTM, but I didn't dive too deep. I don't see anything concerning, but it might be feasible to ask @code-asher for another look.

[code-asher]

Sorry, did not get a chance to review, I can do it next Monday if we want another pass.