AP-3563/AP-5496: Standardise currency handling across the app

[jsugarman]

What

Standardise currency handling across the app and fix existing bugs

Cash income/outgoings handling
Currency field storing invalid values

Standardise currency field handling

Certain currency/amount fields accept humanized monetary
values while others did not. Some would accept but clean
£ and , values such that £1,000 would become 1000
while others would error. Yet others would ignore £ and , values
for validation purposes but when persisting this data they would not, resulting
in, for example, £2,000 becoming a stored value of 2.0.

This PR standardise the approach, removing £ and , values prior to saving
across regular incomes, regular outgoings, cash incomes, cash outgoings,
state benefits, housing benefit, student finance and mandatory and discretionary
capital disregards monetary amount fields.

In should be noted that some forms validate currency, which ignores
£ and , chars, while others do not validate this way. This has not been
changed.

Checklist

Before you ask people to review this PR:

• Tests and rubocop should be passing: bundle exec rake
• Github should not be reporting conflicts; you should have recently run git rebase main.
• The standards in the Git Workflow document on Confluence should be followed
• There should be no unnecessary whitespace changes. These make diffs harder to read and conflicts more likely.
• The PR description should say what you changed and why, with a link to the JIRA story.
• You should have looked at the diff against main and ensured that nothing unexpected is included in your changes.
• You should have checked that the commit messages say why the change was made.

[colinbruce]

Looks okay to me, but maybe it would be better to get input from design to ensure consistent errors and handling?

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud