add Hellō provider

[dickhardt]

Summary

Adds Hellō (https://issuer.hello.coop) as an IdP for email

1683

Release Note

Adding issuer.hello.coop to Fulcio

Hellō meets the requirements defined in https://github.com/sigstore/fulcio/blob/main/docs/new-idp-requirements.md

• Issuer keys are managed by KMS, rotated automatically every 30 days.
• 'sigstore' client is configured, and works with localhost redirect and device flow
• all emails are verified
• sub is a GUID generated on each new user

Documentation

Not at this time

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 48.61%. Comparing base (cf238ac) to head (d13772a). Report is 108 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1684 +/- ## ========================================== - Coverage 57.93% 48.61% -9.33% ========================================== Files 50 67 +17 Lines 3119 4042 +923 ========================================== + Hits 1807 1965 +158 - Misses 1154 1862 +708 - Partials 158 215 +57 ```

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[dickhardt]

@bobcallaway @haydentherapper -- next steps for this PR?

This would increase the options developers have if they want to opt into using Hellō.