feat: .httpie file

[gszr]

First, thank you for this amazing tool :-)

Here's a (vibe-coded) POC for .httpie, a per-project file that sets always-sent headers - or other request parts. If you are lazy like me and do not want to keep inserting the same request headers / params over and over.

Sample:

{
  "headers": {
    "Authorization": "Bearer asdasdasdasdads"
  }
}

Then Authorization will always be sent in httpie requests - but can still be overridden if explicitly given.

Let me know what you think, happy to clean this up, pursue a different direction, or close the PR if this isn't of interest.