feat: support personal tokens (#116)

Description

Support personal tokens:

• add the Platform API client to ensure that personal token has proper permissions.
• update configuration and add flag to enable personal tokens
• update the authorization middleware

Related issue

#116

Examples

...
# Postgres.ai Platform integration.
platform:
  # API URL.
  url: "https://postgres.ai/api/general"

  # Token for authorization in Platform API. This token can be obtained in Postgres.ai Console.
  accessToken: "platform_access_token"

  # Enable authorization with personal tokens of the organization's members.
  enablePersonalTokens: false
...

Checklist

• the MR description has been reviewed
• this MR contains text changes and they have been reviewed OR there are no texts changes
• this MR contains GUI/CLI changes and they have been reviewed OR there are no GUI/CLI changes
• this MR contains API changes, specifications reflect those changes and they have been reviewed OR there are no API changes

Closes #116