This commit adds 4 attachments to the Latvian tax report
and an XML export for the tax report (including the attachments).

The attachments are the following
- PVN 1-I: domestic purchase / import
- PVN 1-II: EU purchase
- PVN 1-III: domestic sales / export
- PVN 2: EU sale

The attachments give more details for the tax report.
The lines of the attachments are "transactions"
A "transaction" is identified by the move and the transaction type or document type.
The transaction type is given via a tax tag (see community PR).
- PVN 1-I: transaction type, move
  - Small transactions (< 150€) are aggregated separately under transaction types 'V' or 'T'
    independently of the move
  - 'V': All small transactions of a partner in case the total of all their small transactions reaches 150€
    - There is max 1 line per partner
  - 'T': All small transactions that are not grouped under some 'V' line
    - There is max 1 line like this; it has no partner information
- PVN 1-II: transaction type, move
  - Small transactions (< 150€) are aggregated separately under transaction types 'V' or 'T'
    (like PVN 1-I)
- PVN 1-III: document type, move and line in the main tax report
  - All transactions with (document) type 'X' are aggregated on a single line
  - Small transactions (< 150€) are aggregated separately under document types 'V' or 'T'
    (like PVN 1-I)
  - The line in the main tax report is ignored for 'X' and small transactions
- PVN 2: transaction type, move
  - No aggregation is performed here

Only account move lines that are tagged with a transaction type (1-I, 1-II, 2)
or a relevant tag for the main report (1-III) are shown in the reports.

The tags `Rep` and `C (car)` only take 40% and 50% respectively of the
base amounts. The tax amount is assumed to be split correctly.

task-4251184

Forward-Port-Of: odoo/enterprise#84135