Add a local network probe to trigger local network privacy dialog

[buggmagnet]

It's all in the title

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This change is 

[linear]

IOS-465 Trigger the local network alert before trying local connections when testing API via proxies

[rablador]

Reviewed 4 of 4 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved

[mojganii]

Reviewable status: all files reviewed, 2 unresolved discussions (waiting on @buggmagnet)

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ios/MullvadVPN/AccessMethodRepository/LocalNetworkProbe.swift line 26 at r1 (raw file):

            using: .udp
        )
        localIpv6Connection.start(queue: dispatchQueue)

What will happen if the connection establishment fails? This part establishes a UDP connection to trigger the dialog. Is there any impact when the user doesn't allow the app access to the local network? Does the app (access methods) work fine if access is restricted?

Moreover, is there any specific reason the type of connection is just UDP? Is it for bypassing ISPs?

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ios/MullvadVPN/Supporting Files/Info.plist line 6 at r1 (raw file):

<dict>
	<key>NSLocalNetworkUsageDescription</key>
	<string>The app needs this to connect and test a new method.</string>

@emils is the description decribtive enough for users?

[mojganii]

Reviewable status: complete! all files reviewed, all discussions resolved

[buggmagnet]

Reviewable status: complete! all files reviewed, all discussions resolved

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ios/MullvadVPN/AccessMethodRepository/LocalNetworkProbe.swift line 26 at r1 (raw file):

What will happen if the connection establishment fails?
Not much, we don't do anything with the connection.

Is there any impact when the user doesn't allow the app access to the local network?
Yes, the user defined custom methods likely won't work, this is why we trigger this here

Moreover, is there any specific reason the type of connection is just UDP?
We don't send any traffic here so it doesn't matter what type of connection it is. But since UDP is "fire and forget", we don't need to have anyone listening on the other end to trigger the warning.

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ios/MullvadVPN/Supporting Files/Info.plist line 6 at r1 (raw file):

Previously, mojganii wrote…

@emils is the description decribtive enough for users?

This was a suggestion from Matilda which Emils approved in the office.