Remove trailing slash on instanceURL

[lcampos]

What does this PR do?

In Windows, we experience issues initializing the Apex Interactive Debugger because the url we build to connect to the Streaming API has an additional slash, making it an invalid url. The changes here strip the trailing slash of the host url.

What issues does this PR fix or reference?

#722, @W-5622038@

[AnanyaJha]

Yay!!

[codecov]

Codecov Report

Merging #751 into develop will decrease coverage by 0.01%.
The diff coverage is 50%.

@@             Coverage Diff             @@
##           develop     #751      +/-   ##
===========================================
- Coverage    74.23%   74.22%   -0.02%     
===========================================
  Files          163      163              
  Lines         6609     6610       +1     
  Branches      1039     1040       +1     
===========================================
  Hits          4906     4906              
  Misses        1433     1433              
- Partials       270      271       +1

Impacted Files	Coverage Δ
...forcedx-apex-debugger/src/core/streamingService.ts	97.22% <50%> (-2.78%)	⬇️

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