Added exporters interfaces page

[DGabri]

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• I have signed the ntop Contributor License Agreement at https://github.com/ntop/legal/blob/main/individual-contributor-licence-agreement.md
• I have read the contributing guide lines https://github.com/ntop/ntopng/blob/dev/CONTRIBUTING.md
• I have updated the documentation (in doc/src/) to reflect the changes made (if applicable)

Link to the related issue:

Describe changes:

Added exporters interfaces page. You can find how data is expected by the frontend in: pro/scripts/lua/rest/v2/get/exporters/exporters_interfaces.lua {
nprobe_ip = "192.168.1.4",
exporter_ip = "10.0.0.4",
interface_id = 4,
in_bytes = 250000,
out_bytes = 125000
}