feat(saml): add SignatureMethod config for SAML IDP (#10520)

# Which Problems Are Solved
When a SAML IDP is created, the signing algorithm defaults to
`RSA-SHA1`.
This PR adds the functionality to configure the signing algorithm while
creating or updating a SAML IDP. When nothing is specified, `RSA-SHA1`
is the default.

Available options:
* RSA_SHA1
* RSA_SHA256
* RSA_SHA512

# How the Problems Are Solved

By introducing a new optional config to specify the Signing Algorithm.

# Additional Changes
N/A

# Additional Context
- Closes #9842

An existing bug in the UpdateSAMLProvider API will be fixed as a
followup in a different
[PR](https://github.com/zitadel/zitadel/pull/10557).

---------

Co-authored-by: Stefan Benz <46600784+stebenz@users.noreply.github.com>
(cherry picked from commit 255d42da65)

cmd/setup/config.go

@@ -157,6 +157,7 @@ type Steps struct {
 	s58ReplaceLoginNames3View               *ReplaceLoginNames3View
 	s59SetupWebkeys                         *SetupWebkeys
 	s60GenerateSystemID                     *GenerateSystemID
+	s61IDPTemplate6SAMLSignatureAlgorithm   *IDPTemplate6SAMLSignatureAlgorithm
 }
 
 func MustNewSteps(v *viper.Viper) *Steps {