Add always-forward config to proxy server

[benbjohnson]

This pull request adds a proxy config setting to specify regex-matching paths to always forward to the primary (even when using GET & HEAD methods). This was proposed on this Fly.io Community forum post.

Usage

proxy:
  always-forward:
    - "^/my/path$"
    - "^/my/other/path$"

[sbbu]

Hello, the Fly.io thread is locked so I'll reply here.. Tested this and it works like a charm!

Adding

proxy:
  always-forward:
    - "/api/auth/callback/*"

to my litefs.yml solved my issue flawlessly. Love this addition!! Thank you!

[benbjohnson]

Ah! Sorry about that. Thanks for following up here. Glad to hear it's working!