Promote upstream TLS changelog entry from minor to major

[tsaarni]

After #5828 was merged (Thank You @KauzClay!) it occurred to me that we could promote the change from minor to major category, to call out the maximum TLS protocol version update. All information was there already, but I think it could be good to highlight it as a major change, since users might observe some differences with their upstream services after upgrade, when TLS handshake selects TLSv1.3. In worst case users could even have some minor problems due to the gaps in Envoy's retry handling, described in envoyproxy/envoy#9300.

[tsaarni]

@KauzClay could you review this since I'm proposing change to your changelog entry? Thank you 😄

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (a579ec3) 78.70% compared to head (c9ce1e9) 78.70%.

Additional details and impacted files

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##             main    #6033   +/-   ##
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  Coverage   78.70%   78.70%           
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  Files         138      138           
  Lines       19717    19717           
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  Hits        15518    15518           
  Misses       3895     3895           
  Partials      304      304           

[KauzClay]

@tsaarni cool, I see what you're saying about potential surprised when connections opt to 1.3.

Your changes make sense to me 👍