[feature/internal/httpclient] add option to configure outgoing protocol (#4134)

# Description

Adds a configuration option to set the outgoing transport of HTTP requests for testing purposes.

## Checklist

- [x] I/we have read the [GoToSocial contribution guidelines](https://codeberg.org/superseriousbusiness/gotosocial/src/branch/main/CONTRIBUTING.md).
- [ ] I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
- [x] I/we have not leveraged AI to create the proposed changes.
- [x] I/we have performed a self-review of added code.
- [x] I/we have written code that is legible and maintainable by others.
- [ ] I/we have commented the added code, particularly in hard-to-understand areas.
- [x] I/we have made any necessary changes to documentation.
- [ ] I/we have added tests that cover new code.
- [ ] I/we have run tests and they pass locally with the changes.
- [ ] I/we have run `go fmt ./...` and `golangci-lint run`.
  - Note: `go fmt` yes, golangci-lint fails, can't load any configuration

Reviewed-on: https://codeberg.org/superseriousbusiness/gotosocial/pulls/4134
Reviewed-by: kim <gruf@noreply.codeberg.org>
Co-authored-by: famfo <famfo@famfo.xyz>
Co-committed-by: famfo <famfo@famfo.xyz>

example/config.yaml

@@ -1113,6 +1113,15 @@ http-client:
   # Default: false
   tls-insecure-skip-verify: false
 
+  # Bool. Sets outgoing queries to webfinger, host-meta and nodeinfo to use
+  # HTTP instead of HTTPS.
+  #
+  # THIS SETTING SHOULD BE USED FOR TESTING ONLY! DO NOT CHANGE THIS SETTING
+  # UNLESS YOU KNOW EXACTLY WHAT YOU'RE DOING AND WHY YOU'RE DOING IT.
+  #
+  # Default: false
+  insecure-outgoing: false
+
 #############################
 ##### ADVANCED SETTINGS #####
 #############################