refactor: pass context for goroutine shutdown

[0xERR0R]

• pass context to server/resolvers
• each goroutine checks for cancellation
• I think, maybe we'll need it for config reload -> we can just close the context and recreate all resolvers

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
cache/expirationcache/expiration_cache.go	100.00% <100.00%> (ø)
cache/expirationcache/prefetching_cache.go	100.00% <100.00%> (ø)
cmd/serve.go	95.16% <100.00%> (+0.24%)	⬆️
config/config.go	78.57% <100.00%> (+0.36%)	⬆️
lists/list_cache.go	95.65% <100.00%> (ø)
querylog/database_writer.go	100.00% <100.00%> (ø)
resolver/blocking_resolver.go	96.14% <100.00%> (+0.05%)	⬆️
resolver/bootstrap.go	95.47% <100.00%> (+0.02%)	⬆️
resolver/caching_resolver.go	94.68% <100.00%> (+0.11%)	⬆️
resolver/client_names_resolver.go	100.00% <100.00%> (ø)
... and 4 more

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[ThinkChaos]

This is great!

[kwitsch]

Agreed this looks really great. 👍