[FIX] account_bank_statement_import_camt: no currency rate found

It seems banks don't have the same convention, some are putting journal's currency
in SrcCcy and others in TgtCcy, so we should inspect both indifferently.
In both cases though, the currency rate provided is to be used in the same way, we
only need to invert it in case the currency rate is provided in the counter value
element.

opw-2664732
opw-2665467
opw-2666160

-------------------------------------------------------------------------------------

[FIX] account_bank_statement_import_camt: improve amount currency set

Before this commit, we were only looking in InstdAmt element to retrieve the
foreign currency and its related amount that are set on statement lines after.
We should also inspect TxAmt and Amt elements, as those can also be set with
a foreign currency. This will allow an easier reconciliation later as the
information about the foreign currency used is not lost and correctly imported.

Forward-Port-Of: odoo/enterprise#22077
Forward-Port-Of: odoo/enterprise#21730