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/repository/authrequest/auth_request.go

@@ -30,6 +30,7 @@ type AddedEvent struct {
 	Scope            []string                  `json:"scope,omitempty"`
 	Audience         []string                  `json:"audience,omitempty"`
 	ResponseType     domain.OIDCResponseType   `json:"response_type,omitempty"`
+	ResponseMode     domain.OIDCResponseMode   `json:"response_mode,omitempty"`
 	CodeChallenge    *domain.OIDCCodeChallenge `json:"code_challenge,omitempty"`
 	Prompt           []domain.Prompt           `json:"prompt,omitempty"`
 	UILocales        []string                  `json:"ui_locales,omitempty"`
@@ -57,6 +58,7 @@ func NewAddedEvent(ctx context.Context,
 	scope,
 	audience []string,
 	responseType domain.OIDCResponseType,
+	responseMode domain.OIDCResponseMode,
 	codeChallenge *domain.OIDCCodeChallenge,
 	prompt []domain.Prompt,
 	uiLocales []string,
@@ -79,6 +81,7 @@ func NewAddedEvent(ctx context.Context,
 		Scope:            scope,
 		Audience:         audience,
 		ResponseType:     responseType,
+		ResponseMode:     responseMode,
 		CodeChallenge:    codeChallenge,
 		Prompt:           prompt,
 		UILocales:        uiLocales,