feat: add discoverable webauthn

[jonas-jonas]

Related issue(s)

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
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• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

[jonas-jonas]

This likely needs a better solution.

We want to add "webauthn" to any identifier field shown on the login page, so the browser can show the autofil UI. But with this change, the webauthn strategy no longer renders an id input field.

[codecov]

Codecov Report

Merging #3567 (a2962c4) into master (df18c09) will decrease coverage by 0.06%.
Report is 12 commits behind head on master.
The diff coverage is 85.92%.

❗ Current head a2962c4 differs from pull request most recent head b5afc35. Consider uploading reports for the commit b5afc35 to get more accurate results

@@            Coverage Diff             @@
##           master    #3567      +/-   ##
==========================================
- Coverage   78.18%   78.13%   -0.06%     
==========================================
  Files         341      341              
  Lines       23052    23136      +84     
==========================================
+ Hits        18023    18077      +54     
- Misses       3679     3697      +18     
- Partials     1350     1362      +12     

Files	Coverage Δ
cmd/clidoc/main.go	69.58% <100.00%> (+0.12%)	⬆️
driver/config/config.go	83.37% <100.00%> (+0.04%)	⬆️
identity/credentials_webauthn.go	100.00% <100.00%> (ø)
identity/extension_credentials.go	91.48% <100.00%> (+3.98%)	⬆️
identity/test/pool.go	99.57% <100.00%> (ø)
schema/errors.go	90.87% <100.00%> (ø)
selfservice/flow/login/flow.go	95.40% <100.00%> (ø)
selfservice/flow/verification/flow.go	88.67% <100.00%> (ø)
selfservice/hook/show_verification_ui.go	100.00% <100.00%> (ø)
selfservice/hook/web_hook.go	80.41% <100.00%> (ø)
... and 17 more

... and 2 files with indirect coverage changes