Develop a way to specify header values from on_* methods of subclasses of `BaseFederationServerServlet`

[H-Shay]

Currently when instantiating a subclass of BaseFederationServerServlet, and calling one of it's on_* methods the same arguments are passed in for all functions, resulting in needing to special-case when a function requires different arguments (ie see the discussion at https://github.com/element-hq/synapse/pull/17172/files/b6803f6049a823ca2c76da129c790728257e4ef4#r1594778790). Is there a more graceful way to do this?