[18.0][ADD] fleet_vehicle_analytic_purchase: add new module

[CristianoMafraJunior]

@Escodoo HT02193

Summary

Adds fleet_vehicle_analytic_purchase, a new module linking fleet vehicles to
analytic accounts (cost centers) and exposing the purchase orders that share
one of those accounts directly from the vehicle form.

Why

fleet.vehicle has no built-in way to track which analytic account(s) /
cost center(s) a vehicle belongs to, and there is no built-in way to jump
from a vehicle to the purchase orders associated with it. Separately,
analytic_distribution (on purchase.order / purchase.order.line) is
stored as JSON, so it doesn't get the usual "type and pick a suggested
record" Many2one search experience in the UI — only plain text matching.

What it does

• Adds analytic.mixin to fleet.vehicle, so each vehicle can carry an
  analytic_distribution (one or more cost centers).
• Adds a "Purchase Orders" stat button on the vehicle form, showing the
  count of purchase orders that share an analytic account with the vehicle,
  with an action to open them filtered accordingly.
• Adds a small, non-stored, search-only analytic_account_id Many2one field
  (via a shared analytic.account.search.mixin) on purchase.order and
  purchase.order.line, redirecting search to the existing
  distribution_analytic_account_ids field. This gives Requests for
  Quotation, Purchase Orders and Purchase Order Lines search views the same
  "pick a suggested record" UX already used for Vendor/Product, without
  duplicating or storing any data.
• Exposes analytic_account_id in the three search views above.

Dependencies

Depends on purchase_analytic_global for the header-level
analytic_distribution field on purchase.order (rather than
purchase_analytic, which provides the same field through a separate,
overlapping implementation — using both in the same database duplicates the
field and its compute/inverse logic).

cc @marcelsavegnago @WesleyOliveira98 @MarcusPDL @medicegabriel

[marcelsavegnago]

LGTM

[WesleyOliveira98]

LGTM

[OCA-git-bot]

This PR has the approved label and has been created more than 5 days ago. It should therefore be ready to merge by a maintainer (or a PSC member if the concerned addon has no declared maintainer). 🤖