Add UI for Tax Zone and Tax Rates

[arjun289]

Why?

Admin should be able to create new tax zones from the admin panel and modify settings for the same. Also, the tax rates for a tax zone should be configurable from the admin panel.

This change addresses the need by:

• Adds UI for tax zones.
• Adds UI to handle tax rates for a tax zone.
• Add/modify tax rate model to cater for new requirements.

Comments

• Makes extensive use of nested layouts to handle UI.
• In the tax_rate_class_values schema, I have to populate the changeset data with tax_class and tax_class_id if the changes contain tax_class_id. This was done because tax_rate_class_values is being handled using cast_assoc in tax_rate schema and, these values are required to render the UI properly.

[delivers#163283477]

Checklist

• [ ] I have read CONTRIBUTING.md.
• [ ] My code follows the style guidelines of this project.
• [ ] I have commented my code, particularly in hard-to-understand areas.
• [ ] My code does not generate any (new) credo and compile-time warnings.
• [ ] I have updated the documentation wherever necessary.
• [ ] I have added tests to cover my changes.

[codecov[bot]]

Codecov Report

Merging #456 into develop will decrease coverage by 0.03%. The diff coverage is 75%.

@@             Coverage Diff             @@
##           develop     #456      +/-   ##
===========================================
- Coverage    77.86%   77.82%   -0.04%     
===========================================
  Files          174      174              
  Lines         2128     2138      +10     
===========================================
+ Hits          1657     1664       +7     
- Misses         471      474       +3

Impacted Files	Coverage Δ
...s/snitch_core/lib/core/data/schema/tax/tax_zone.ex	100% <ø> (ø)	:arrow_up:
apps/snitch_core/lib/core/data/model/zone/zone.ex	65.78% <0%> (-3.66%)	:arrow_down:
...ps/snitch_core/lib/core/data/model/tax/tax_rate.ex	100% <100%> (ø)	:arrow_up:
...ps/snitch_core/lib/core/data/model/tax/tax_zone.ex	100% <100%> (ø)	:arrow_up:
...e/lib/core/data/schema/tax/tax_rate_class_value.ex	85.71% <83.33%> (-14.29%)	:arrow_down:

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 4dc2523...a1b337f. Read the comment docs.