feat: tweaks to UpsertSessions

[alnr]

• fix: don't update immutable columns when upserting sessions
• fix: don't emit SessionIssued and SessionChanged events multiple times when retrying database transactions

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 78.01%. Comparing base (e942507) to head (2a0d1d1).

Files	Patch %	Lines
persistence/sql/persister_session.go	75.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3878      +/-   ##
==========================================
- Coverage   78.05%   78.01%   -0.04%     
==========================================
  Files         360      360              
  Lines       25232    25239       +7     
==========================================
- Hits        19694    19691       -3     
- Misses       4032     4040       +8     
- Partials     1506     1508       +2     

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