fix(oidc): store requested response_mode (#8145)

# Which Problems Are Solved

Zitadel never stored or returned the requested `response_mode` in oidc
Auth Requests. This caused the oidc library to fallback to the default
based on the response_type.

# How the Problems Are Solved

- Store the `response_mode` in the Auth request repo
- Store the `response_mode` in the Auth request v2 events
- Return the `resonse_mode` from the Auth Request v1 and v2
`ResponseMode()` methods. (Was hard-coded to an empty string)

# Additional Changes

- Populate the `response_modes_supported` to the oidc Discovery
Configuration. When it was empty, the standard specifies the default of
`query` and `fragment`. However, our oidc library also supports
`form_post` and by this fix, zitadel now also supports this.

# Additional Context

- Closes #6586
- Reported
https://discord.com/channels/927474939156643850/1151508313717084220

---------

Co-authored-by: Livio Spring <livio.a@gmail.com>

internal/command/auth_request.go

@@ -21,6 +21,7 @@ type AuthRequest struct {
 	Scope            []string
 	Audience         []string
 	ResponseType     domain.OIDCResponseType
+	ResponseMode     domain.OIDCResponseMode
 	CodeChallenge    *domain.OIDCCodeChallenge
 	Prompt           []domain.Prompt
 	UILocales        []string
@@ -64,6 +65,7 @@ func (c *Commands) AddAuthRequest(ctx context.Context, authRequest *AuthRequest)
 		authRequest.Scope,
 		authRequest.Audience,
 		authRequest.ResponseType,
+		authRequest.ResponseMode,
 		authRequest.CodeChallenge,
 		authRequest.Prompt,
 		authRequest.UILocales,
@@ -162,6 +164,7 @@ func authRequestWriteModelToCurrentAuthRequest(writeModel *AuthRequestWriteModel
 			Scope:         writeModel.Scope,
 			Audience:      writeModel.Audience,
 			ResponseType:  writeModel.ResponseType,
+			ResponseMode:  writeModel.ResponseMode,
 			CodeChallenge: writeModel.CodeChallenge,
 			Prompt:        writeModel.Prompt,
 			UILocales:     writeModel.UILocales,