Add missing headers and claims for Mercure JWT when using v1

[acelaya]

Part of shlinkio/shlink#2671

This PR expands the changes from #186, adding some missing claims and headers on generated mercure JWT when using v1.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.31%. Comparing base (6caf796) to head (9df7290).
⚠️ Report is 4 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #187      +/-   ##
============================================
+ Coverage     99.29%   99.31%   +0.01%     
- Complexity      183      184       +1     
============================================
  Files            49       49              
  Lines           569      584      +15     
============================================
+ Hits            565      580      +15     
  Misses            4        4              

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