RGW: add delay injection options for integration testing

RGW: add delay injection options for integration testing

Introduce two developer-level configuration options for controlled delay
injection during integration testing:

  - rgw_inject_delay_sec: duration of the injected delay (in seconds)
  - rgw_inject_delay_pattern: pattern to select which delay points are
    activated

These options help reproduce timing-sensitive or race conditions in a
deterministic way during RGW integration tests.

In the future, these options may evolve to support more complex timing
scenarios by using list or map types. This would allow multiple delay
injection points to be configured simultaneously, for example: delaying
pattern A by 5 seconds, pattern B before or after a specific event, or
using different durations for each point.

Signed-off-by: Oguzhan Ozmen <oozmen@bloomberg.net>