fix(Log): add aria-label to close button

[marstamm]

Proposed Changes

Make close button accessible.

closes #177

Steps to reproduce:

• check out branch
• open log
• check AXE dev tools
• no Buttons must have discernible Text Issue is shown

Checklist

To ensure you provided everything we need to look at your PR:

• Brief textual description of the changes present
• Visual demo attached No visual changes
• Steps to try out present, i.e. using the @bpmn-io/sr tool
• Related issue linked via Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}