Explicitly bind to localhost in docs serve

### Housekeeping

- [X] I am a maintainer of dbt-core

### Short description

Explicitly bind to localhost in docs serve

### Acceptance criteria

Explicitly bind to localhost in docs serve

### Suggested Tests

ensure tcp server was explicitly set port to localhost

### Impact to Other Teams

N/A

### Will backports be required?

yes - 1.8, 1.7, 1.6

### Context

_No response_