Pragma: no-cache header

[douxxtech]

Added the Pragma: no-cache header: https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Pragma

It is only set if the MAX_AGE config is set to 0.

[github-actions]

threads: 4 (auto), conns: 50, duration: 20s

[wrk]
Running 20s test @ http://127.0.0.1:8080/
  4 threads and 50 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     4.87ms   10.62ms 419.47ms   99.50%
    Req/Sec     1.77k   409.24     2.85k    70.00%
  139053 requests in 20.03s, 209.13MB read
  Socket errors: connect 0, read 126, write 0, timeout 0
Requests/sec:   6940.66
Transfer/sec:     10.44MB