Improve strategies logic

[idotta]

Note

Standardizes multi-tenant strategy configuration and aligns codebase with new keys/defaults.

• Replace option key constants with strategy-name keys in StrategyOptions and rename defaults: DefaultHeaderName→DefaultHeader, DefaultClaimType→DefaultClaim
• Update tenant resolution wiring to use new keys in ServiceCollectionExtensions (WithHeaderStrategy, WithRouteStrategy, WithClaimStrategy)
• Adjust ValidateBearerTokenTenantMiddleware, CurrentUserService, and IdmtUserClaimsPrincipalFactory to read claim/header names via new keys; make IsActive check case-insensitive
• Extend sample appsettings*.json with StrategyOptions overrides for header and claim
• Update tests to reflect new constants/keys and to read header name from IdmtOptions in IdmtApiFactory

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