Feat/func/add ReservedConcurrentExecutions to globals

[merzwilliam]

Issue #, if available: #760

Description of changes: Added "ReservedConcurrentExecutions" to the list of supported global properties for the AWS::Serverless::Function resource. PR also includes updates to relevant tests and an update to the Globals support doc.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-io]

Codecov Report

Merging #808 into develop will decrease coverage by 0.3%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #808      +/-   ##
===========================================
- Coverage    94.85%   94.54%   -0.31%     
===========================================
  Files           67       67              
  Lines         2952     2824     -128     
  Branches       576      508      -68     
===========================================
- Hits          2800     2670     -130     
- Misses          76       81       +5     
+ Partials        76       73       -3

Impacted Files	Coverage Δ
samtranslator/plugins/globals/globals.py	100% <ø> (ø)	⬆️
samtranslator/plugins/api/implicit_api_plugin.py	96.26% <0%> (-3.74%)	⬇️
samtranslator/model/api/api_generator.py	96.17% <0%> (-1.88%)	⬇️
samtranslator/model/eventsources/push.py	88.73% <0%> (-1.57%)	⬇️
samtranslator/model/intrinsics.py	94.44% <0%> (-1.02%)	⬇️
samtranslator/model/sam_resources.py	96.09% <0%> (-0.88%)	⬇️
samtranslator/sdk/resource.py	100% <0%> (ø)	⬆️
samtranslator/model/__init__.py	96.85% <0%> (+0.36%)	⬆️
samtranslator/swagger/swagger.py	98.32% <0%> (+0.39%)	⬆️
samtranslator/model/eventsources/pull.py	92% <0%> (+0.47%)	⬆️

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[brettstack]

Thanks @merzwilliam! One final thing, could you please add this Global to this test https://github.com/awslabs/serverless-application-model/blob/master/tests/translator/input/globals_for_function.yaml.

[merzwilliam]

@brettstack - I apologize for taking so long to make this change! Should be good to go now =)

[jlhood]

Thanks so much for this contribution!