refactor: Simplify url embeddings logic in Ingest admin app page

[superhindupur]

Purpose

This PR removes more logic out of the Ingest admin app page and into the backend function, adding unit tests for the newly added logic in the function.

It also adds back the changes from PR #789 that were mistakenly reverted in a previous PR.

Does this introduce a breaking change?

[ ] Yes
[x ] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

Deploy the admin app and the function. Test ingesting URLs with and without integrated vectorization.

[github-actions[bot]]

Coverage Report •

File	Stmts	Miss	Cover	Missing
code/backend/batch
AddURLEmbeddings.py	47	0	100%
BatchStartProcessing.py	18	0	100%
code/backend/pages
01_Ingest_Data.py	70	70	0%	1–10, 12–14, 16, 22, 29, 32–33, 36–39, 41–44, 48–50, 53–55, 58–65, 68–70, 72, 75–78, 81, 86–88, 90–91, 93–94, 97–98, 102–104, 109–112, 119–120, 125, 131–132
TOTAL	2252	676	69%

Tests	Skipped	Failures	Errors	Time
167	0 :zzz:	0 :x:	0 :fire:	10.029s :stopwatch:

[ross-p-smith]

This will conflict with #798 - any chance we can work on getting that one in first?