[PM-20592] [PM-22737] [PM-22738] Send grant validator (#6151)

**feat**: create `SendGrantValidator` and initial `SendPasswordValidator` for Send access grants  
**feat**: add feature flag to toggle Send grant validation logic  
**feat**: add Send client to Identity and update `ApiClient` to generic `Client`  
**feat**: register Send services in DI pipeline  
**feat**: add claims management support to `ProfileService`  
**feat**: distinguish between invalid grant and invalid request in `SendAccessGrantValidator`

**fix**: update parsing of `send_id` from request  
**fix**: add early return when feature flag is disabled  
**fix**: rename and organize Send access scope and grant type  
**fix**: dotnet format

**test**: add unit and integration tests for `SendGrantValidator`  
**test**: update OpenID configuration and API resource claims

**doc**: move documentation to interfaces and update inline comments  

**chore**: add TODO for future support of `CustomGrantTypes`

src/Identity/IdentityServer/RequestValidators/SendAccess/ISendPasswordRequestValidator.cs

@@ -0,0 +1,16 @@
+using Bit.Core.Tools.Models.Data;
+using Duende.IdentityServer.Validation;
+
+namespace Bit.Identity.IdentityServer.RequestValidators.SendAccess;
+
+public interface ISendPasswordRequestValidator
+{
+    /// <summary>
+    /// Validates the send password hash against the client hashed password.
+    /// If this method fails then it will automatically set the context.Result to an invalid grant result.
+    /// </summary>
+    /// <param name="context">request context</param>
+    /// <param name="resourcePassword">resource password authentication method containing the hash of the Send being retrieved</param>
+    /// <returns>returns the result of the validation; A failed result will be an error a successful will contain the claims and a success</returns>
+    GrantValidationResult ValidateSendPassword(ExtensionGrantValidationContext context, ResourcePassword resourcePassword, Guid sendId);
+}