Refactor the subscriptions api to meet standard mount approach

[otherview]

Description

This ticket refactors the handlesubject into the websocked method.

Fixes # (issue)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• New and existing E2E tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have not added any vulnerable dependencies to my code

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 78.75000% with 17 lines in your changes missing coverage. Please review.

Project coverage is 60.95%. Comparing base (5867f22) to head (00b0597).

Files with missing lines	Patch %	Lines
api/subscriptions/subscriptions.go	87.93%	5 Missing and 2 partials ⚠️
thorclient/wsclient/client.go	40.00%	4 Missing and 2 partials ⚠️
api/utils/http.go	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #926      +/-   ##
==========================================
+ Coverage   60.81%   60.95%   +0.13%     
==========================================
  Files         220      220              
  Lines       23414    23431      +17     
==========================================
+ Hits        14240    14283      +43     
+ Misses       8007     7982      -25     
+ Partials     1167     1166       -1     

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[libotony]

Appended a minor naming commit @otherview