DISPATCH-1290: add simple http healthcheck

[grs]

and allow websockets to be disabled on http listener

[codecov-io]

Codecov Report

Merging #468 into master will decrease coverage by 0.05%.
The diff coverage is 10%.

@@            Coverage Diff             @@
##           master     #468      +/-   ##
==========================================
- Coverage   86.95%   86.89%   -0.06%     
==========================================
  Files          86       86              
  Lines       19067    19068       +1     
==========================================
- Hits        16580    16570      -10     
- Misses       2487     2498      +11

Impacted Files	Coverage Δ
src/router_core/router_core.c	87.09% <0%> (+0.02%)	⬆️
src/connection_manager.c	89.32% <100%> (ø)	⬆️
src/remote_sasl.c	82.77% <0%> (-1.12%)	⬇️
src/router_core/transfer.c	90.93% <0%> (-0.57%)	⬇️
src/router_core/agent_link.c	67.01% <0%> (-0.52%)	⬇️
src/router_core/connections.c	94.3% <0%> (-0.25%)	⬇️
src/iterator.c	93.45% <0%> (-0.23%)	⬇️
src/router_node.c	94.05% <0%> (-0.13%)	⬇️
src/container.c	79.62% <0%> (+0.18%)	⬆️
... and 1 more

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