Support specific country code inside tax combos

[samlown]

• This large PR ensures that the customer-rates tag included in an invoice will copy the customer's tax ID country to each individual tax row, thus ensuring that the customer's tax rates are applied.
• In order to support this, it made sense to remove the restrictions around tax regimes, its now possible to create a GOBL invoice for any country in the world, albeit with reduced validation processes.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 79.55556% with 46 lines in your changes missing coverage. Please review.

Project coverage is 77.75%. Comparing base (c37c170) to head (88fa587). Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
tax/regime.go	6.66%	10 Missing and 4 partials :warning:
tax/combo.go	91.74%	5 Missing and 4 partials :warning:
bill/invoice.go	80.00%	4 Missing and 4 partials :warning:
regimes/fr/tax_identity.go	0.00%	2 Missing and 1 partial :warning:
bill/invoice_correct.go	60.00%	1 Missing and 1 partial :warning:
tax/identity.go	84.61%	1 Missing and 1 partial :warning:
tax/totals.go	66.66%	1 Missing and 1 partial :warning:
regimes/ch/tax_identity.go	0.00%	0 Missing and 1 partial :warning:
regimes/co/tax_identity.go	0.00%	0 Missing and 1 partial :warning:
regimes/es/tax_identity.go	0.00%	0 Missing and 1 partial :warning:
... and 3 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #347 +/- ## ========================================== + Coverage 77.20% 77.75% +0.54% ========================================== Files 179 180 +1 Lines 8068 8105 +37 ========================================== + Hits 6229 6302 +73 + Misses 1480 1460 -20 + Partials 359 343 -16 ```

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