OIN SSO doc refactor

[thomascavanagh-okta]

Description:

• What's changed? Refactors oin-sso-overview and redistributes its content into concepts/sso-overview and concepts/multi-tenancy. Updates all internal links, redirects, and navbar to point to the new locations.
• Is this PR related to a Monolith release? No

Resolves:

• OKTA-1175626

Netlify Preview Link:

https://tc-okta-1175626-oin-refactor-sso--dev-docs-preview.netlify.app/docs/concepts/sso-overview/

[okta-prod-github-app]

Acrolinx score

A minimum Acrolinx Score of 80 is required. The total score is an average of the subscores.
Select Total score to review the Acrolinx scorecard for your article. Try to increase your individual scores, for example: Correctness. Your content will be clearer and more consistent.

Article	Total score Required:80	Word and phrases (Brand, terms) Preferred: 80	Correctness (Spelling, grammar) Preferred: 80	Clarity (Readability) Preferred: 80	Inclusive language (+ accesibility) Preferred: 80
✅ packages/@okta/vuepress-site/docs/concepts/multi-tenancy/index.md	90	96	96	79
✅ packages/@okta/vuepress-site/docs/concepts/sso-overview/index.md	94	100	92	83
✅ packages/@okta/vuepress-site/docs/guides/build-sso-integration/main/index.md	93	100	81	100
✅ packages/@okta/vuepress-site/docs/guides/build-sso-integration/main/openidconnect/prep.md	87	96	83	73
✅ packages/@okta/vuepress-site/docs/guides/create-an-app-integration/main/index.md	93	100	94	83
✅ packages/@okta/vuepress-site/docs/guides/index.md	87	67	80	78
✅ packages/@okta/vuepress-site/docs/guides/submit-app-prereq/main/index.md	82	98	78	74
✅ packages/@okta/vuepress-site/docs/guides/submit-oin-app/main/openidconnect/protocol-supported.md	88	100	65	100

Successfully checked 8 of 8 documents.
See summary in Content Analysis Dashboard

Reopen the pull request or push new changes to check again.

Depending on the Acrolinx server configuration, the
links expire after some time and you must have a login for the
Acrolinx server to access them again.