Add opis URL to Beamline model

[OCopping]

This will allow for the user to manually define the URL address of the k8s opis directories.
It can also hopefully be used to help fetch the pvi screens for embedded screens.

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.89%. Comparing base (fb3ebb4) to head (cecfe61).
⚠️ Report is 9 commits behind head on main.

Files with missing lines	Patch %	Lines
src/techui_builder/models.py	91.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
+ Coverage   81.72%   81.89%   +0.17%     
==========================================
  Files           9        9              
  Lines         673      685      +12     
==========================================
+ Hits          550      561      +11     
- Misses        123      124       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.