Make SentryAppender non-final for Log4j2 and Logback (#1602)

[cocorossello]

📜 Description

Make SentryAppender non-final for Log4j2 and Logback

💡 Motivation and Context

Users will be able to customize the appenders it if they need it. See #1602

💚 How did you test it?

Did a full build (I had to disable OutboxSenderTest class, deserialize sample envelope with event and two attachments test, SentryWebfluxIntegrationTest (due to an Error while closing the hub), but I believe those are not related to to my changes at all.

📝 Checklist

• I reviewed the submitted code
• I added tests to verify the changes
• I updated the docs if needed
• No breaking changes

🔮 Next steps

[marandaneto]

thanks @cocorossello :)

[codecov-commenter]

Codecov Report

Merging #1603 (983eb3f) into main (fb12011) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               main    #1603   +/-   ##
=========================================
  Coverage     76.07%   76.07%           
  Complexity     1976     1976           
=========================================
  Files           198      198           
  Lines          6842     6842           
  Branches        680      680           
=========================================
  Hits           5205     5205           
  Misses         1305     1305           
  Partials        332      332           

Impacted Files	Coverage Δ
...src/main/java/io/sentry/log4j2/SentryAppender.java	85.54% <ø> (ø)
...rc/main/java/io/sentry/logback/SentryAppender.java	89.02% <100.00%> (ø)

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