fix: Return badRequest if trying to terminate an environment that has already been terminated

[nguyen102]

Issue #, if available:

Description of changes:
If an environment is in the TERMINATED, TERMINATING, or TERMINATING_FAILED status and a request is made to terminate the environment, return an HTTP Status Code 400 error.

Checklist:

• Have you successfully deployed to an AWS account with your changes?
• Have you written new tests for your core changes, as applicable?

AS review ticket id:

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

[codecov]

Codecov Report

Merging #946 (d8dd26d) into develop (99cc33b) will increase coverage by 0.01%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #946      +/-   ##
===========================================
+ Coverage    51.44%   51.45%   +0.01%     
===========================================
  Files          295      295              
  Lines        16784    16790       +6     
  Branches      2596     2599       +3     
===========================================
+ Hits          8634     8640       +6     
  Misses        7163     7163              
  Partials       987      987              

Impacted Files	Coverage Δ
...ironment/service-catalog/environment-sc-service.js	70.46% <0.00%> (+0.37%)	⬆️

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[maghirardelli]

LGTM