Add a timeout to every CI step to halt hung builds

[huonw]

If a step in build hangs or takes an unusually long time, previously CI would let it continue, occupying machines forever. In lieu of a global timeout (buildkite/feedback#170, https://forum.buildkite.community/t/pipeline-timeouts/722), we can manually apply a timeout to every step, as a last resort to catch slow/hung builds. This uses the timeout_in_minutes optional attribute:

The number of minutes a job created from this step is allowed to run. If the job does not finish within this limit, it will be automatically canceled and the build will fail.

Our steps currently range from 30 seconds to 8 minutes, so 30 minutes should be a safe "something serious is wrong" time-out.

See: #905

[codeclimate]

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[huonw]

Example build with timeouts reduced to 2 minutes as a test: https://buildkite.com/stellar/stellargraph-public/builds/1596

[kieranricardo]

nice - 30 minutes seems like a safe timeout to apply to all the steps 👍

[stellar-graph-bot]

Codecov Report

Merging #906 into develop will decrease coverage by 0.4%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           develop    #906     +/-   ##
=========================================
- Coverage     85.3%   84.9%   -0.4%     
=========================================
  Files           51      51             
  Lines         5189    5026    -163     
=========================================
- Hits          4427    4266    -161     
+ Misses         762     760      -2     

Impacted Files	Coverage Δ
stellargraph/core/graph.py	98.5% <0.0%> (-0.1%)	⬇️

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