[Feature/SessionStats] Endpoint to fetch session data

[Alathreon]

Pull-request

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

Changes

• [ ] Existing code
• [X] 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
    }
]