Allow shipping service backend/frontend URLs to be set separately

[gfrn]

JIRA ticket: LIMS-1751

Summary:

Since these may be different (especially when dealing with network topologies which have filters/blocks on them), anyone deploying SCAUP can now set different frontend/backend URLs.

Changes:

• Allow shipping service backend/frontend URLs to be set separately

To test:

• Go to https://local-oidc-test.diamond.ac.uk:9000/proposals/bi23047/sessions/100/shipments/117/booking-and-labels, click "view shipping information", check if the redirect URL matches the value set in shipping_service.frontend_url instead of backend_url

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.84%. Comparing base (456ab10) to head (f91f6e5).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #3      +/-   ##
==========================================
- Coverage   93.89%   93.84%   -0.06%     
==========================================
  Files          38       38              
  Lines        1475     1478       +3     
==========================================
+ Hits         1385     1387       +2     
- Misses         90       91       +1     

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[ndg63276]

LGTM