Add target domain to extauth proto

[jmhbh]

Description

• This PR modifies extauth proto to add the target_domain field to InternalSession and RedisSession under UserSession.
• The purpose of making these changes is so a user applying a authz policy using OIDC can specify a target domain that they want to be stored in a cookie which is then used to validate the request domain to ensure that they match.
• Tests/use for this api change can be found in this PR

Context

• In this issue Qualcomm wants to include the target domain in the OIDC cookie and use this domain to validate requests in order to prevent cookie replay attacks.

Checklist:

• I included a concise, user-facing changelog (for details, see https://github.com/solo-io/go-utils/tree/master/changelogutils) which references the issue that is resolved.
• If I updated APIs (our protos) or helm values, I ran make -B install-go-tools generated-code to ensure there will be no code diff
• I followed guidelines laid out in the Gloo Edge contribution guide
• I opened a draft PR or added the work in progress label if my PR is not ready for review
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works

[solo-changelog-bot]

Issues linked to changelog:
https://github.com/solo-io/ext-auth-service/issues/314

[jmhbh]

/kick

[github-actions]

Visit the preview URL for this PR (updated for commit afd0ed6):

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[jackstine]

LGTM!