feat: trusted (instance) domains (#8369)

# Which Problems Are Solved

ZITADEL currently selects the instance context based on a HTTP header
(see https://github.com/zitadel/zitadel/issues/8279#issue-2399959845 and
checks it against the list of instance domains. Let's call it instance
or API domain.
For any context based URL (e.g. OAuth, OIDC, SAML endpoints, links in
emails, ...) the requested domain (instance domain) will be used. Let's
call it the public domain.
In cases of proxied setups, all exposed domains (public domains) require
the domain to be managed as instance domain.
This can either be done using the "ExternalDomain" in the runtime config
or via system API, which requires a validation through CustomerPortal on
zitadel.cloud.

# How the Problems Are Solved

- Two new headers / header list are added:
- `InstanceHostHeaders`: an ordered list (first sent wins), which will
be used to match the instance.
(For backward compatibility: the `HTTP1HostHeader`, `HTTP2HostHeader`
and `forwarded`, `x-forwarded-for`, `x-forwarded-host` are checked
afterwards as well)
- `PublicHostHeaders`: an ordered list (first sent wins), which will be
used as public host / domain. This will be checked against a list of
trusted domains on the instance.
- The middleware intercepts all requests to the API and passes a
`DomainCtx` object with the hosts and protocol into the context
(previously only a computed `origin` was passed)
- HTTP / GRPC server do not longer try to match the headers to instances
themself, but use the passed `http.DomainContext` in their interceptors.
- The `RequestedHost` and `RequestedDomain` from authz.Instance are
removed in favor of the `http.DomainContext`
- When authenticating to or signing out from Console UI, the current
`http.DomainContext(ctx).Origin` (already checked by instance
interceptor for validity) is used to compute and dynamically add a
`redirect_uri` and `post_logout_redirect_uri`.
- Gateway passes all configured host headers (previously only did
`x-zitadel-*`)
- Admin API allows to manage trusted domain

# Additional Changes

None

# Additional Context

- part of #8279 
- open topics: 
  - "single-instance" mode
  - Console UI

internal/query/instance.go

@@ -195,19 +195,24 @@ var (
 	instanceByIDQuery string
 )
 
-func (q *Queries) InstanceByHost(ctx context.Context, host string) (_ authz.Instance, err error) {
+func (q *Queries) InstanceByHost(ctx context.Context, instanceHost, publicHost string) (_ authz.Instance, err error) {
 	ctx, span := tracing.NewSpan(ctx)
 	defer func() {
 		if err != nil {
-			err = fmt.Errorf("unable to get instance by host %s: %w", host, err)
+			err = fmt.Errorf("unable to get instance by host: instanceHost %s, publicHost %s: %w", instanceHost, publicHost, err)
 		}
 		span.EndWithError(err)
 	}()
 
-	domain := strings.Split(host, ":")[0] // remove possible port
-	instance, scan := scanAuthzInstance(host, domain)
-	err = q.client.QueryRowContext(ctx, scan, instanceByDomainQuery, domain)
-	logging.OnError(err).WithField("host", host).WithField("domain", domain).Warn("instance by host")
+	instanceDomain := strings.Split(instanceHost, ":")[0] // remove possible port
+	publicDomain := strings.Split(publicHost, ":")[0]     // remove possible port
+	instance, scan := scanAuthzInstance()
+	// in case public domain is the same as the instance domain, we do not need to check it
+	// and can empty it for the check
+	if instanceDomain == publicDomain {
+		publicDomain = ""
+	}
+	err = q.client.QueryRowContext(ctx, scan, instanceByDomainQuery, instanceDomain, publicDomain)
 	return instance, err
 }
 
@@ -216,7 +221,7 @@ func (q *Queries) InstanceByID(ctx context.Context) (_ authz.Instance, err error
 	defer func() { span.EndWithError(err) }()
 
 	instanceID := authz.GetInstance(ctx).InstanceID()
-	instance, scan := scanAuthzInstance("", "")
+	instance, scan := scanAuthzInstance()
 	err = q.client.QueryRowContext(ctx, scan, instanceByIDQuery, instanceID)
 	logging.OnError(err).WithField("instance_id", instanceID).Warn("instance by ID")
 	return instance, err
@@ -421,8 +426,6 @@ type authzInstance struct {
 	iamProjectID        string
 	consoleID           string
 	consoleAppID        string
-	host                string
-	domain              string
 	defaultLang         language.Tag
 	defaultOrgID        string
 	csp                 csp
@@ -453,14 +456,6 @@ func (i *authzInstance) ConsoleApplicationID() string {
 	return i.consoleAppID
 }
 
-func (i *authzInstance) RequestedDomain() string {
-	return strings.Split(i.host, ":")[0]
-}
-
-func (i *authzInstance) RequestedHost() string {
-	return i.host
-}
-
 func (i *authzInstance) DefaultLanguage() language.Tag {
 	return i.defaultLang
 }
@@ -492,11 +487,8 @@ func (i *authzInstance) Features() feature.Features {
 	return i.features
 }
 
-func scanAuthzInstance(host, domain string) (*authzInstance, func(row *sql.Row) error) {
-	instance := &authzInstance{
-		host:   host,
-		domain: domain,
-	}
+func scanAuthzInstance() (*authzInstance, func(row *sql.Row) error) {
+	instance := &authzInstance{}
 	return instance, func(row *sql.Row) error {
 		var (
 			lang                  string