Add: DataChannel Latency Test

[gingernaz]

Relevant components:

• Signalling server
• Frontend library
• Frontend UI library
• Matchmaker
• Platform scripts
• SFU

Problem statement:

Measure data channel latency

Solution

Introducing a new test that will show data channel latency values

Documentation

To start the test:

• Open stats panel
• Hit Run Test button under Data Channel Latency Test
• Wait for the results

Test Plan and Compatibility

Compatible with the latest main

[lukehb]

Just confirming backwards compatibility is preserved?

For example, are the following cases met:

1. For users on older versions of UE does this silently fail (if so, good!)?
2. Likewise, for the UE side changes, if they are using the old frontend (without this change) does it still stream no problems (if so good!).

[gingernaz]

Just confirming backwards compatibility is preserved?

For example, are the following cases met:

1. For users on older versions of UE does this silently fail (if so, good!)?
2. Likewise, for the UE side changes, if they are using the old frontend (without this change) does it still stream no problems (if so good!).

Just double-checked this.
Users with older versions of UE will get NaN values with the test. Users of the older frontend are still able to stream with no problems.

[gingernaz]

Can we please drop this PR in favour of #315