snowykte0426 260d298cc5 Add Migration Guide from Spring Security SAML Extension
This adds a dedicated migration guide for users moving from the Spring Security SAML Extension to the built-in SAML 2.0 support.

Includes:
- Content migrated from the project wiki
- xref links for `saml2Login`, `saml2Logout`, and `saml2Metadata`
- Metadata example moved to Examples Matrix
- Cleanup and naming per review feedback

Closes gh-11161

Signed-off-by: snowykte0426 <snowykte0426@naver.com>
2025-05-15 17:17:43 -06:00
..
2023-06-16 20:23:19 -05:00