global: add support for specifying known proxies (#63)

* Add KNOWN_PROXIES

* Add known proxy setup in Startup.cs

Refactor forwarded headers configuration to use a variable for options.

* Document KNOWN_PROXIES in .env file

Added documentation for KNOWN_PROXIES environment variable

* Clean up

Restored license comments and formatting in Constants.cs.

* Apply suggestion from @thecodrr

* Added KnownProxies functionality at Streetwriters.Common level

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Co-authored-by: Abdullah Atta <thecodrr@protonmail.com>

.env

@@ -46,6 +46,11 @@ TWILIO_SERVICE_SID=
 # Example: https://app.notesnook.com,http://localhost:3000
 NOTESNOOK_CORS_ORIGINS=
 
+# Description: Add known proxies for incoming HTTP requests
+# Required: no
+# Example: 192.168.1.2,192.168.1.3
+KNOWN_PROXIES=
+
 # Description: This is the public URL for the web app, and is used by the backend for creating redirect URLs (e.g. after email confirmation etc). 
 # Note: the URL has no slashes at the end
 # Required: yes