Fix the urlpatterns for the metrics app to address warnings

[rosswhitfield]

Description of the changes

This will fix the warning during webmon startup (urls.W002) Your URL pattern '/' [name='metrics'] has a route beginning with a '/'. Remove this slash as it is unnecessary. If this pattern is targeted in an include(), ensure the include() pattern has a trailing '/'.

To test start up webmon and check that the warning is no longer there docker logs data_workflow-webmon-1

Also verify that the metrics still work as expected, see #186

Check all that apply:

• updated documentation
• Source added/refactored
• Added unit tests
• Added integration tests
• (If applicable) Verified that manual tests requiring the /SNS and /HFIR filesystems pass without fail

References:

• Links to IBM EWM items: 8007: [WebMon] Fix warnings when starting up WebMon
• Links to related issues or pull requests:

Manual test for the reviewer

(Instructions for testing here)

Check list for the reviewer

• best software practices
  • clearly named variables (better to be verbose in variable names)
  • code comments explaining the intent of code blocks
• All the tests are passing
• The documentation is up to date
• code comments added when explaining intent

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 77.78%. Comparing base (de13b21) to head (15ad755).

Additional details and impacted files

@@           Coverage Diff           @@
##             next     #199   +/-   ##
=======================================
  Coverage   77.78%   77.78%           
=======================================
  Files          54       54           
  Lines        4708     4708           
=======================================
  Hits         3662     3662           
  Misses       1046     1046           

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