[BE1] Federation Data Exchange

[arnauds5]

• Add federation tokens exchange handler
• Avoid duplicate websocket connections in federation of multiple LAOs within one server
• Add the server socket to the list of server sockets and use NewServerSocket instead of NewClientSocket
• Fix missing federation result message if the same server is used
• handle challenge msg of a federation init directly instead of using a websocket if only one server

[github-actions[bot]]

Pull reviewers stats

Stats of the last 30 days for popstellar:		User	Total reviews	Time to review	Total comments
	K1li4nL 🥇	19 ▀▀▀▀▀	1d 20h 18m)) ▀	14 ▀▀▀
	arnauds5 🥈	5 ▀	18h 5m))	4 ▀
	emonnin-epfl 🥉	4 ▀	8h 20m))	8 ▀▀
	onsriahi14	3 ▀	1d 10h 51m))	4 ▀
	MariemBaccari	2 ▀	22h 39m))	6 ▀
	simone-kalbermatter	2 ▀	5h 32m))	0
	matteosz	2 ▀	1d 5h 29m))	3 ▀
	1florentin	1	19d 1h 53m)) ▀▀▀▀▀	0
	sgueissa	1	49m))	3 ▀
	quadcopterman	1	10d 7h 3m)) ▀▀▀	0

^{⚡️ Pull request stats}

[github-actions[bot]]

🟠 There seems to be some formatting issues that must be applied from PR https://github.com/dedis/popstellar/pull/1947 first.

[sonarcloud[bot]]

Quality Gate passed for 'PoP - PoPCHA-Web-Client'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarcloud[bot]]

Quality Gate passed for 'PoP - Be2-Scala'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarcloud[bot]]

Quality Gate passed for 'PoP - Be1-Go'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
82.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sonarcloud[bot]]

Quality Gate passed for 'PoP - Fe2-Android'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[sgueissa]

LGTM