- version update to 2.4.48

Changes with Apache 2.4.48
*) mod_proxy_wstunnel: Add ProxyWebsocketFallbackToProxyHttp to opt-out the
fallback to mod_proxy_http for WebSocket upgrade and tunneling.
[Yann Ylavic]
*) mod_proxy: Fix flushing of THRESHOLD_MIN_WRITE data while tunneling.
BZ 65294. [Yann Ylavic]
*) core: Fix a regression that stripped the ETag header from 304 responses.
PR 61820 [Ruediger Pluem, Roy T. Fielding]
*) core: Adding SSL related inquiry functions to the server API.
These function are always available, even when no module providing
SSL is loaded. They provide their own "shadowing" implementation for
the optional functions of similar name that mod_ssl and impersonators
of mod_ssl provide.
This enables loading of several SSL providing modules when all but
one of them registers itself into the new hooks. Two old-style SSL
modules will not work, as they replace the others optional functions
with their own.
Modules using the old-style optional functions will continue to work
as core supplies its own versions of those.
The following has been added so far:
- ap_ssl_conn_is_ssl() to query if a connection is using SSL.
- ap_ssl_var_lookup() to query SSL related variables for a
server/connection/request.
- Hooks for 'ssl_conn_is_ssl' and 'ssl_var_lookup' where modules
providing SSL can install their own value supplying functions.
- ap_ssl_add_cert_files() to enable other modules like mod_md to provide
certificate and keys for an SSL module like mod_ssl.
- ap_ssl_add_fallback_cert_files() to enable other modules like mod_md to