haproxy: update to 2.2.4.

[zdykstra]

Assume maintainership, enable the prometheus-exporter service and bump to the latest LTS (2.1 is EOL in Q1 2021)

[ericonr]

Cross build to armv7l-musl:

In file included from include/haproxy/stream-t.h:33,                                     
                 from include/haproxy/http_ana.h:29,                                     
                 from include/haproxy/connection.h:30,                                   
                 from include/haproxy/ssl_sock.h:27,                                     
                 from src/ssl_utils.c:18:                                                
include/haproxy/hlua-t.h: At top level:                                                  
include/haproxy/hlua-t.h:27:10: fatal error: lua.h: No such file or directory            
   27 | #include <lua.h>                                                                 
      |          ^~~~~~~                                                                 
compilation terminated.                                                                  
make: *** [Makefile:870: src/ssl_utils.o] Error 1                                        

It also has a lot of warnings about alignment.

[zdykstra]

I guess I should get a cross compile environment setup so I can fix this.

[zdykstra]

Native and cross builds finishing here without any warnings/errors.

[jnbr]

no need to wait for slow CI then