Stunner - [VSCode] Support for process metadata attributes

The goal for this task is to be able to add or remove attributes for the BPMN model (process). This way the user will be able to manage generic attributes for the process by the use of a new table component.

This will allow, for instance, to add support for the securityRoles attribute, as the user will be able to add a new generic attribute with key "securityRoles " and the given value.

The UI field for the generic attributes will be similar to the following one, but with the titles "Attribute"/"Value", and both being regular input fields, and also with the "Remove" icon on each row.

Acceptance criteria:

• Update the process model to add suport for generic attributes
• Generic attributes values will be of type String (keys as well, so it can be considered a Map of Strings)
• Proide a new form field to add or remove generics attributes
  • The component will be presented as a table, where users can perform CRUD operations for the key/values
  • The component wlil be placed in the Advanced tab for the process (on top of Global Variables)
  • The label for the componoent will be "Metadata"
• Marshalling - those generic attributes must be un/serializaed to the BPMN file as well

PS:
Related to KOGITO-373, where we annotate endpoint with the specified security role.
Sample model attached.