Add note about Datadog.configure requiring block in 1.x to Upgrade Guide

[ivoanjo]

Spotted this change when working with @lloeki on validating 1.0.0.beta2.

[lloeki]

LGTM

[ivoanjo]

@delner any concerns about this change?

[delner]

I don't really see this particular change as constructive or useful. It calls out a weird usage that was employed as a hack as if it's meant to be used this way.

I wouldn't recommend this. If the hack was predicated by some flaw, it would be better to address that flaw.

[ivoanjo]

@delner Since this is something that changed (and even bit us!) it seems nice to have it documented as a change in the "Breaking Changes" section -- it is an actual breaking change in the public API.

But I do agree that by itself, calling Datadog.configure shouldn't be useful or needed. So what're your thoughts on instead of suggesting:

Use Datadog.configure { } instead.

we suggest:

Remove usages of Datadog.configure without a block.

[ivoanjo]

Updated PR with the advice to remove such uses.

[codecov-commenter]

Codecov Report

Merging #1970 (ce9017b) into master (60ecc8a) will increase coverage by 0.15%.
The diff coverage is 93.96%.

@@            Coverage Diff             @@
##           master    #1970      +/-   ##
==========================================
+ Coverage   97.53%   97.69%   +0.15%     
==========================================
  Files         998     1001       +3     
  Lines       49006    50453    +1447     
==========================================
+ Hits        47800    49291    +1491     
+ Misses       1206     1162      -44     

Impacted Files	Coverage Δ
.../datadog/appsec/contrib/rack/request_middleware.rb	34.48% <25.00%> (+10.95%)	⬆️
lib/datadog/appsec/processor.rb	86.20% <86.20%> (ø)
spec/datadog/core/error_spec.rb	94.02% <90.00%> (-0.38%)	⬇️
lib/datadog/ci/contrib/rspec/example.rb	96.96% <100.00%> (+0.41%)	⬆️
spec/datadog/appsec/processor_spec.rb	100.00% <100.00%> (ø)
...c/datadog/ci/contrib/rspec/instrumentation_spec.rb	100.00% <100.00%> (ø)
...c/datadog/ci/contrib/rspec/some_shared_examples.rb	100.00% <100.00%> (ø)
spec/datadog/profiling/ext/forking_spec.rb	99.39% <0.00%> (-0.61%)	⬇️
lib/datadog/ci/test.rb	100.00% <0.00%> (ø)
lib/datadog/ci/flush.rb	100.00% <0.00%> (ø)
... and 214 more

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[marcotc]

I've used this pattern before, specially when trying to run the host application test with ddtrace enabled.

[ivoanjo]

I spoke with David a week back and he was happy with the alternative advice; merging this in.