fix(op): export NewProvider to allow customized issuer

[muhlemmer]

#478 allows to customize header used for the issuer host. However, it did not provide means to expose this options to the provider constructor..

This change exports NewPriovider so that the issuer function can be passed directly and therefore be customized.
It also deprecates the other constructors as they became redundant.

Definition of Ready

• I am happy with the code
• Short description of the feature/issue is added in the pr description
• PR is linked to the corresponding user story
• Acceptance criteria are met
• All open todos and follow ups are defined in a new ticket and justified
• Deviations from the acceptance criteria and design are agreed with the PO and documented.
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• Critical parts are tested automatically
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[codecov]

Codecov Report

Merging #479 (7a7e593) into main (7475023) will not change coverage.
The diff coverage is 50.00%.

@@           Coverage Diff           @@
##             main     #479   +/-   ##
=======================================
  Coverage   60.29%   60.29%           
=======================================
  Files          78       78           
  Lines        6753     6753           
=======================================
  Hits         4072     4072           
  Misses       2385     2385           
  Partials      296      296           

Files	Coverage Δ
pkg/op/op.go	69.84% <50.00%> (ø)

[github-actions]

🎉 This PR is included in version 3.2.1 🎉

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