* implement default values for header directive
closes#3804
* remove `set_default` header op and rely on "require" handler instead
This has the following advantages over the previous attempt:
- It does not introduce a new operation for headers, but rather nicely
extends over an existing feature in the header handler.
- It removes the need to specify the header as "deferred" because it is
already implicitely deferred by the use of the require handler. This
should be less confusing to the user.
* add integration test for header directive in caddyfile
* bubble up errors when parsing caddyfile header directive
* don't export unnecessarily and don't canonicalize headers unnecessarily
* fix response headers not passed in blocks
* caddyfile: fix clash when using default header in block
Each header is now set in a separate handler so that it doesn't clash
with other headers set/added/deleted in the same block.
* caddyhttp: New idle_timeout default of 5m
* reverseproxy: fix random hangs on http/2 requests with server push (#3875)
see https://github.com/golang/go/issues/42534
* Refactor and cleanup with improvements
* More specific link
Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>
Co-authored-by: Денис Телюх <telyukh.denis@gmail.com>
