support query params and json output on GET /contiainers

[runleveldev]

This pull request improves the /containers endpoint by adding support for filtering containers using query parameters and by allowing clients to request a JSON response if preferred. These changes enhance the flexibility and usability of the API.

Improvements to API filtering and response format:

• The where clause in the Container.findAll query now merges req.session.user with any query parameters in req.query, allowing clients to filter containers by additional fields.
• The endpoint now checks the client's Accept header and returns a JSON response if application/json is preferred over text/html, improving support for API consumers.