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/domain/oidcresponsemode_enumer.go

@@ -0,0 +1,86 @@
+// Code generated by "enumer -type OIDCResponseMode -transform snake -trimprefix OIDCResponseMode"; DO NOT EDIT.
+
+package domain
+
+import (
+	"fmt"
+	"strings"
+)
+
+const _OIDCResponseModeName = "unspecifiedqueryfragmentform_post"
+
+var _OIDCResponseModeIndex = [...]uint8{0, 11, 16, 24, 33}
+
+const _OIDCResponseModeLowerName = "unspecifiedqueryfragmentform_post"
+
+func (i OIDCResponseMode) String() string {
+	if i < 0 || i >= OIDCResponseMode(len(_OIDCResponseModeIndex)-1) {
+		return fmt.Sprintf("OIDCResponseMode(%d)", i)
+	}
+	return _OIDCResponseModeName[_OIDCResponseModeIndex[i]:_OIDCResponseModeIndex[i+1]]
+}
+
+// An "invalid array index" compiler error signifies that the constant values have changed.
+// Re-run the stringer command to generate them again.
+func _OIDCResponseModeNoOp() {
+	var x [1]struct{}
+	_ = x[OIDCResponseModeUnspecified-(0)]
+	_ = x[OIDCResponseModeQuery-(1)]
+	_ = x[OIDCResponseModeFragment-(2)]
+	_ = x[OIDCResponseModeFormPost-(3)]
+}
+
+var _OIDCResponseModeValues = []OIDCResponseMode{OIDCResponseModeUnspecified, OIDCResponseModeQuery, OIDCResponseModeFragment, OIDCResponseModeFormPost}
+
+var _OIDCResponseModeNameToValueMap = map[string]OIDCResponseMode{
+	_OIDCResponseModeName[0:11]:       OIDCResponseModeUnspecified,
+	_OIDCResponseModeLowerName[0:11]:  OIDCResponseModeUnspecified,
+	_OIDCResponseModeName[11:16]:      OIDCResponseModeQuery,
+	_OIDCResponseModeLowerName[11:16]: OIDCResponseModeQuery,
+	_OIDCResponseModeName[16:24]:      OIDCResponseModeFragment,
+	_OIDCResponseModeLowerName[16:24]: OIDCResponseModeFragment,
+	_OIDCResponseModeName[24:33]:      OIDCResponseModeFormPost,
+	_OIDCResponseModeLowerName[24:33]: OIDCResponseModeFormPost,
+}
+
+var _OIDCResponseModeNames = []string{
+	_OIDCResponseModeName[0:11],
+	_OIDCResponseModeName[11:16],
+	_OIDCResponseModeName[16:24],
+	_OIDCResponseModeName[24:33],
+}
+
+// OIDCResponseModeString retrieves an enum value from the enum constants string name.
+// Throws an error if the param is not part of the enum.
+func OIDCResponseModeString(s string) (OIDCResponseMode, error) {
+	if val, ok := _OIDCResponseModeNameToValueMap[s]; ok {
+		return val, nil
+	}
+
+	if val, ok := _OIDCResponseModeNameToValueMap[strings.ToLower(s)]; ok {
+		return val, nil
+	}
+	return 0, fmt.Errorf("%s does not belong to OIDCResponseMode values", s)
+}
+
+// OIDCResponseModeValues returns all values of the enum
+func OIDCResponseModeValues() []OIDCResponseMode {
+	return _OIDCResponseModeValues
+}
+
+// OIDCResponseModeStrings returns a slice of all String values of the enum
+func OIDCResponseModeStrings() []string {
+	strs := make([]string, len(_OIDCResponseModeNames))
+	copy(strs, _OIDCResponseModeNames)
+	return strs
+}
+
+// IsAOIDCResponseMode returns "true" if the value is listed in the enum definition. "false" otherwise
+func (i OIDCResponseMode) IsAOIDCResponseMode() bool {
+	for _, v := range _OIDCResponseModeValues {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}