chore(battery_plus): Update Kotlin, Gradle and add Dependabot config

[vbuberen]

Description

Same as #1261 - updating Kotlin, Gradle and adding a Dependabot config for Android dependencies.

This is the final one in the series of Kotlin/Gradle updates so far till I migrate rest of packages to Kotlin.

Related Issues

#1248
#1222

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I titled the PR using Conventional Commits.
• I did not modify the CHANGELOG.md nor the pubspec.yaml files.
• All existing and new tests are passing.
• The analyzer (flutter analyze) does not report any problems on my PR.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change (please indicate that with a ! in the title as explained in Conventional Commits).
• No, this is not a breaking change.