Adds functionality to re-request the Service Access Information

[dsilhavy]

• Adds a new ClientSessionModel class to save all information about a running streaming session. We use a hashmap to map a client id to an instance of this new model class
• Parses the headers from the ServiceAccessInformation response of the AF (M5)
• Starts a timer that re-requests the ServiceAccessInformation based on max-age in the cache-control header
• Compares the current values of the etag and the last-modified headers to the previous ones. If nothing changed the ServiceAccessInformation is not updated and the timer is reset according to max-age
• Sends previous etag and last-modified header values as If-None-Match and If-Modified-Since request headers.

This needs more testing once our Linode instance is back. For the implementation I did a quick check with a local server:

Response headers:

res.set({
        'ETag': '12345',
        'last-modified': Date.now(),
        'cache-control': 'max-age=10, test=20'
})

Request headers:

{if-none-match: "12345", if-modified-since: "1690985040545"}

This addresses #30