Add authCookieName option for mercure

[acelaya]

Part of shlinkio/shlink#2671

Yet another PR to expand on the integration with Mercure 1.0, after #186, #187 and #188

This one adds one extra option so that people can let Shlink know what is the cookie name set in Mercure Hub for the auth token.

This will be later used to expose to web clients, so that they can set the right cookie when subscribing to updates.

Additionally, it renames the MercureVersion cases from v0 and v1 to legacy and stable, so that it is future-proof for later mercure stable versions..

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.31%. Comparing base (ed5162b) to head (33fc865).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #189   +/-   ##
=========================================
  Coverage     99.31%   99.31%           
- Complexity      183      184    +1     
=========================================
  Files            49       49           
  Lines           581      585    +4     
=========================================
+ Hits            577      581    +4     
  Misses            4        4           

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