option to mark function/procedure parameters with security flag

[OndrejValenta]

• security flag describes the sensitivity level of given parameter
• security levels are 'none', 'secure', 'strict', 'omit'
• security levels can be used in code generation for secure logging
• none level means parameter can be safely added to log message
• secure level means parameter can be added to log message based on configuration value 'db-gen:insecure-logging'. When this value is true, parameter is added to log as plain text, when false parameter is added to log as **
• strict level means parameter is always added to log as **
• omit level means parameter is always omitted from any log

[FilipJakab]

The list of these parameters could be specified globally. For example all "password" params should be hidden and then per-procedure's config would have higher precedence...