Bump dash from 0.34.0 to 2.15.0 in /boilerplates/dash

Bumps [dash](https://github.com/plotly/dash) from 0.34.0 to 2.15.0.
- [Release notes](https://github.com/plotly/dash/releases)
- [Changelog](https://github.com/plotly/dash/blob/dev/CHANGELOG.md)
- [Commits](plotly/dash@v0.34.0...v2.15.0)

---
updated-dependencies:
- dependency-name: dash
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

boilerplates/dash/requirements.txt

@@ -1,7 +1,7 @@
 certifi==2023.7.22
 chardet==3.0.4
 click==6.7
-dash==0.34.0
+dash==2.15.0
 dash-core-components==0.27.1
 dash-html-components==0.11.0
 dash-renderer==0.13.0