make configurable in which part of the OIDC exchange custom claims should be sent

从 OIDC-to-SAML 属性映射表开始，跟踪将 custom claims 发送到 userinfo endpoint 或 id_token 的 authorization code flow。定义映射如何支持向后兼容的 userinfo 默认值，然后确定显式的 client claims 参数应如何与已配置的目标交互。完成的标准是：每个已配置的 custom claim 都能被正确路由，同时不改变现有默认值。

In the authorization code flow, custom claims can be sent either in the "id_token" or by querying the "userinfo".

If the client made a preference as to where the claims should be by setting the "claims parameter", the module honours this and sends accordingly.

If no preference is indicated by the client, the module currently sends custom claims always via the userinfo endpoint. As per OIDC core spec, the claims /could/ alternatively be sent directly in the id_token.

The issue at hand suggests to make configurable where a specific custom claim should be sent. The suggested place is the OIDC-to-SAML attribute mapping table, as this lists every single claim

Example, for a hypothetical custom claim "foobar":

    // The default translate table from SAML attributes to OIDC claims.
    ModuleConfig::OPTION_AUTH_SAML_TO_OIDC_TRANSLATE_TABLE => [
...
          'foobar' => [
             'attribute' => 'urn:x-randomvendor:attibute-xyz',
             'dest' => 'userinfo' # or 'id_token'
          ],

There should be a backwards-compatible default (single-string array defaults to "userinfo", to keep the current behaviour).

An open question is how to prioritise if the client did send a claim parameter, but the configured destination differs from the configured destination - which one wins?