Implement local error message when table list can't be loaded

[Maren-SSB]

When the table list can't be loaded, a local error message should be displayed in the table list area instead of the table content. (Aka: Improve error handling when PxWebApi is not available.)

The implementation should follow the solution proposal and designs available in Figma: https://www.figma.com/design/UEIiaYcc9VoE7fBZSKrKMh/PxWeb-2.0-Starting-page?node-id=3324-159659&t=S6mhk0xzIE84q2AI-4

Screenshot from Figma:

Acceptance criteria

• When loading the table list fails, the error message "Could not load the tables" is displayed.
• The implementation matches the solution proposal and designs specified in Figma.
• When the table list loads successfully, the error message is not displayed and the tables are shown as normal.
• The implementation complies with WCAG 2.1 Level A and AA requirements.