Add janitor to clean up Cloud Map integration test resources

[astaticvoid]

Issue #, if available: 45

Description of changes:
Create janitor script to clean up all resources under a namespace in Cloud Map, to reset test account in between integration test executions.

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[codecov-commenter]

Codecov Report

Merging #57 (7a85132) into main (075bf73) will increase coverage by 2.66%.
The diff coverage is 80.95%.

@@            Coverage Diff             @@
##             main      #57      +/-   ##
==========================================
+ Coverage   47.70%   50.36%   +2.66%     
==========================================
  Files           9       11       +2     
  Lines        1000     1082      +82     
==========================================
+ Hits          477      545      +68     
- Misses        502      512      +10     
- Partials       21       25       +4     

Impacted Files	Coverage Δ
integration/janitor/main.go	0.00% <0.00%> (ø)
pkg/cloudmap/api.go	62.65% <0.00%> (+0.37%)	⬆️
pkg/cloudmap/aws_facade.go	100.00% <ø> (ø)
integration/janitor/janitor.go	84.41% <84.41%> (ø)
pkg/cloudmap/client.go	54.31% <100.00%> (+0.59%)	⬆️

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[runakash]

Let's just avoid too much of shortening of the function names.

[astaticvoid]

Unreadable clunky abbreviations are idiomatic in go/Unix culture (kubectl? gobcon?), especially for anything we’re not exporting but we can be more verbose like Java.

[astaticvoid]

Refactored ListInstances in API class to return list of instance summaries, in favour of deferring endpoint conversion in the client. This allows us to re-use the call for janitor.
Note that we are returning a list of structs and not pointers, as the summaries from the SDK are now collected without conversion, and we have to be careful not to return a collection of duplicate pointers. Modified a test to ensure ListInstances can return multiple results to catch this. Probably our other list functions should do the same.

[runakash]