[gateway] Rename healthcheck thread

[brasseld]

15:16:31.370 [healthcheck-1] [] DEBUG i.g.g.s.h.EndpointHealthCheck - Runnning health-check for Api{id='4e0db366-f772-4489-8db3-66f772b48989', name='API Bear', version='1'}
15:16:31.370 [healthcheck-1] [] DEBUG i.g.g.s.h.EndpointHealthCheck - Execute health-check request: http://localhost:9099/api/bears/	GET	headers:
15:16:31.373 [AsyncHttpClient-2-13] [] DEBUG i.g.g.s.h.EndpointHealthCheck - An error occurs while executing request http://localhost:9099/api/bears/	GET	headers:: Connection refused: localhost/0:0:0:0:0:0:0:1:9099
15:16:31.373 [AsyncHttpClient-2-13] [] DEBUG i.g.g.s.h.EndpointHealthCheck - Report health results for Api{id='4e0db366-f772-4489-8db3-66f772b48989', name='API Bear', version='1'}
15:16:31.434 [rate-limit-poller] [] DEBUG i.g.g.s.ratelimit.RateLimitPoller - Refresh rate-limits from repository

It will be useful to rename async-http-client thread to something more understandable(healtheck-poller in this case).