feat: Set default issuer in JWT tokens

[mitar]

Proposed changes

This is backwards incompatible change, but it allows one to set default issuer which seems to not be possible otherwise, despite being existing in the DefaultJWTStrategy struct.

Checklist

• I have read the contributing 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
  confirm that I got green light (please contact
  security@ory.sh) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation within the code base (if appropriate)

[aeneasr]

Great, thank you!

[mitar]

Any plans to release/bump version?

[aeneasr]

done v0.32.1 :)