fix(HTTP2Transport): Only enable HTTP2 when DSN is HTTPS

[BYK]

No description provided.

[BYK]

This is the core change. All the rest is refactoring to make this easier to implement.

[codecov]

Codecov Report

Attention: Patch coverage is 85.18519% with 4 lines in your changes missing coverage. Please review.

Project coverage is 84.31%. Comparing base (336b177) to head (7736211).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
sentry_sdk/transport.py	85.18%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3678      +/-   ##
==========================================
- Coverage   84.33%   84.31%   -0.03%     
==========================================
  Files         133      133              
  Lines       14231    14241      +10     
  Branches     2398     2400       +2     
==========================================
+ Hits        12002    12007       +5     
- Misses       1485     1487       +2     
- Partials      744      747       +3     

Files with missing lines	Coverage Δ
sentry_sdk/transport.py	84.05% <85.18%> (-0.63%)	⬇️

... and 3 files with indirect coverage changes

[sentrivana]

lgtm