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_model.go

@@ -23,6 +23,7 @@ type AuthRequestWriteModel struct {
 	Scope            []string
 	Audience         []string
 	ResponseType     domain.OIDCResponseType
+	ResponseMode     domain.OIDCResponseMode
 	CodeChallenge    *domain.OIDCCodeChallenge
 	Prompt           []domain.Prompt
 	UILocales        []string
@@ -58,6 +59,7 @@ func (m *AuthRequestWriteModel) Reduce() error {
 			m.Scope = e.Scope
 			m.Audience = e.Audience
 			m.ResponseType = e.ResponseType
+			m.ResponseMode = e.ResponseMode
 			m.CodeChallenge = e.CodeChallenge
 			m.Prompt = e.Prompt
 			m.UILocales = e.UILocales