Make Import CSV action modal

[ericleponner]

Description

When user create transaction group, they may choose to Import CSV.
This operation is started asynchronously without any modality:

1. user may be leave Create Group form
2. choose Discard
   • operation has no effect
   • Import CSV continues in background
   • user must wait for its completion

Two possible behaviors are expected:

1. Import CSV is a modal operation : it prevents any interaction before completion
2. Back + Discard interrupts Import CSV and really discard new group

Steps to reproduce

1. Start TT
2. Create New > Transaction Group
Description: Nice Group
3. Import CSV
   => use CSV with > 100 rows and many different account ids
   => import action starts
   => transaction counter is incrementing
4. Click Back button
   => Save Group dialog appears
5. Discard
6. Create New > Transaction Group
   => group is not empty
   => CSV import is still on-going
   => Discard action has been ignored : BUG

Additional context

No response

Hedera network

No response

Version

v0.26.0

Operating system

None