fix: swagger for dynamic client registration

[daniel-eichinger-bl]

Fix swagger documentation of the OAuth2 / OpenID Dynamic Client registration.
The endpoint was specified at /connect/register, but Ory Hydra exposes it at /oauth2/register.

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
  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 or changed the documentation.

Further Comments

Once this PR is merged, the documentation should also be updated: Ory Hydra docs
Will sign the CLA once clarified with my superior.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #3141 (d9f14c8) into master (a383b5a) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #3141   +/-   ##
=======================================
  Coverage   79.52%   79.52%           
=======================================
  Files         112      112           
  Lines        7967     7967           
=======================================
  Hits         6336     6336           
  Misses       1225     1225           
  Partials      406      406           

Impacted Files	Coverage Δ
client/handler.go	79.18% <ø> (ø)

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[aeneasr]

Thank you!

[vinckr]

Hello @daniel-eichinger-bl
Congrats on merging your first PR in Ory 🎉 !
Your contribution will soon be helping secure millions of identities around the globe 🌏.
As a small token of appreciation we send all our first time contributors a gift package to welcome them to the community.
Please drop me an email and I will forward you the form to claim your Ory swag!