Create stale.yml for Stale Bot

[srprash]

Issue #, if available:

Description of changes:

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

[codecov-commenter]

Codecov Report

Merging #228 into master will decrease coverage by 0.06%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #228      +/-   ##
==========================================
- Coverage   79.35%   79.29%   -0.07%     
==========================================
  Files          80       80              
  Lines        3158     3158              
==========================================
- Hits         2506     2504       -2     
- Misses        652      654       +2     

Impacted Files	Coverage Δ
aws_xray_sdk/core/sampling/local/reservoir.py	88.88% <0.00%> (-11.12%)	⬇️

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