Rework how we manage the AWS_DEFAULT_REGION

[synfinatic]

• Remove --region from exec & eval commands
• Add --no-region to exec & eval commands
• Never overwrite/clear the AWS_DEFAULT_REGION set by the user

Fixes: #152

[codecov]

Codecov Report

Merging #153 (b96dc6a) into main (570b7b7) will increase coverage by 1.74%.
The diff coverage is 53.19%.

@@            Coverage Diff             @@
##             main     #153      +/-   ##
==========================================
+ Coverage   37.68%   39.43%   +1.74%     
==========================================
  Files           7        7              
  Lines        1186     1202      +16     
==========================================
+ Hits          447      474      +27     
+ Misses        700      692       -8     
+ Partials       39       36       -3     

Impacted Files	Coverage Δ
sso/settings.go	60.46% <53.19%> (+7.15%)	⬆️

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