feat: Add DSN getters

[cleptric]

Unsure about func (dsn Dsn) GetScheme() string instead of func (dsn Dsn) GetScheme() sheme.

I want to avoid exporting type scheme string though 🤔

This is needed for OTel (#537).

[codecov]

Codecov Report

Base: 84.01% // Head: 83.94% // Decreases project coverage by -0.07% ⚠️

Coverage data is based on head (9d97cd6) compared to base (6b68090).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #540      +/-   ##
==========================================
- Coverage   84.01%   83.94%   -0.07%     
==========================================
  Files          23       23              
  Lines        2802     2816      +14     
==========================================
+ Hits         2354     2364      +10     
- Misses        367      370       +3     
- Partials       81       82       +1     

Impacted Files	Coverage Δ
dsn.go	96.29% <100.00%> (+0.42%)	⬆️
integrations.go	89.01% <0.00%> (-2.32%)	⬇️

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