"Limit of 20 addresses reached" is not implemented on mobile

[churik]

Bug Report

Problem

As a user, I want to add my saved addresses within the existing backend limits, since exceeding the limit might lead to unexpected behavior.

Found during implementing functional backend tests in status-im/status-go#6333

Discussion: Thread

The backend imposes a limit of 20 addresses, which can be checked using wakuext_remainingCapacityForSavedAddresses.

Currently, this check is not enforced on Mobile, meaning there is effectively no limit, since wakuext_upsertSavedAddress (used for adding/updating saved addresses) does not apply any restrictions.

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Expected Behavior

How it is used on desktop client:

if (!d.editMode && root.store.remainingCapacityForSavedAddresses() === 0) {
    limitPopup.active = true
    return
}

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Actual Behavior

There is no current behavior, as the screen was not designed for this case.
Could not find it in Figma

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Acceptance Criteria

• Cannot add more than 20 saved addresses per mode
• See an informative pop-up when the limit is reached - should be toast, design added here

[shivekkhurana]

@xAlisher We'll need some figma design for this ux.

UPD: design added