feat(search): add Search API saml provider list endpoint and samlProv…

[mikegron]

SFINT-6504

Adds SAML identity provider support for Search Pages.

• Exposes Platform.search.listSamlIdentityProviders() to retrieve configured providers from the Search API’s /authentication/saml endpoint. (see doc)
• Adds SearchApiSamlIdentityProvider as the response model.
• Adds accesses.samlProvider to Search Page configuration so consumers can persist the selected provider name.

Acceptance Criteria

• My changes are publicly available, documented, and deployed in production. (i.e. on Swagger)
• JSDoc annotates each property added in the exported interfaces
• The proposed changes are covered by unit tests
• Commits containing breaking changes are properly identified as such
• README.md is adjusted to reflect the proposed changes (if relevant)
• My merge commit message will follow the commit guidelines (See Commit Guidelines)

[SimonMilord]

LGTM

[FelixBlaisThon]