Fix the description of the filesystem-realm update-key-pair operation in the Elytron documentation

The documentation for the update-key-pair operation for the filesystem-realm resource can be found here:

https://github.com/wildfly/wildfly/blob/main/docs/src/main/asciidoc/_elytron/components/Filesystem_Security_Realm.adoc

Notice that the example update-key-pair operation currently includes two parameters, key-store and key-store-alias. This is incorrect, this operation doesn't take any parameters.

The proper way to update a key pair is as follows:

/subsystem=elytron/filesystem-realm=keystore:write-attribute(name=key-store, value=newKeystore)
/subsystem=elytron/filesystem-realm=keystore:write-attribute(name=key-store-alias, value=newKeystoreAlias)
/subsystem=elytron/filesystem-realm=fsRealm:update-key-pair()

The documentation should be updated to reflect this.

More details about this operation can be found here:
https://github.com/wildfly-security/wildfly-elytron/pull/1716