[ENHANCEMENT] Tempo: update more-traces-available alert styling

[andreasgerstmayr]

Description

Our UX designer recommended the following changes to the more-traces-available alert:

• move it to the top
• update text
• use warning instead of info
• add a close button

Screenshots

Old:

New:

Checklist

• Pull request has a descriptive title and context useful to a reviewer.
• Pull request title follows the [<catalog_entry>] <commit message> naming convention using one of the
  following catalog_entry values: FEATURE, ENHANCEMENT, BUGFIX, BREAKINGCHANGE, DOC,IGNORE.
• All commits have DCO signoffs.

UI Changes

• Changes that impact the UI include screenshots and/or screencasts of the relevant changes.
• Code follows the UI guidelines.