Add ability to export existing credentials

[simonas-notcat]

Research what would be the best UX to export credentials. Initial ideas:

• The output of /credentials command, could add a Download button to every item in the list. After clicking this button, the list would update with the attachment containing the credentials
• Every item in the list could contain a link to https://community.veramo.io/credential/{hash}

[simonas-notcat]

This can be done simply by opening the public profile of the user in the agent explorer, and exporting credentials there. No need to add this functionality in the bot's UX