[Feature/SessionStats] Endpoint to fetch session data

[Alathreon]

Pull-request

• I have read the contributing guidelines.
• I have read the code guidelines.
• I have created a relating issue.

Changes

• Existing code
• New feature

Closes Issue: NaN

Description

Add an endpoint to fetch the stats of the current sessions.
Exemple:

curl --request GET \
  --url http://localhost:8080/jshell/sessions

[
	{
		"id": "test",
		"timeSinceCreation": 17,
		"timeUntilExpiration": 1782,
		"totalEvalTime": 15,
		"doingOperation": false
	},
	{
		"id": "135178a3-e54f-4bc8-bbe1-2e626b4de50b",
		"timeSinceCreation": 12,
		"timeUntilExpiration": 14,
		"totalEvalTime": 2,
		"doingOperation": false
	}
]