Test with an existing internal proxy

### Problem statement
Customers with stringent security requirements often already have an internal proxy for managing and auditing network access. We need to ensure the allowlist for coder boundary complies with their existing configured proxy. Otherwise our target profile for boundary will experience difficulties on initial setup.

### Proposal
Set up a proxy `proxy.dev.coder.com` (not sure what this looks like) and test the HTTP allowlist in claude code with boundary.