Auto approve and merge pull requests by Dependabot using Github actions

[sophia-guo]

Dependabot auto creates PR to update github actions dependency version. #31

We'd like to approve and merge the pull requests raised by Dependabot. Looks like it's easy to do as there are available github actions available on market place.

https://medium.com/@dileepkumarjami/auto-approve-and-merge-pull-requests-by-dependabot-using-github-actions-468557967fa4

Same request for other github actions: AdopOpenJDK/build-jdk, Eclipse/build-openj9

[sophia-guo]

https://docs.github.com/en/github/administering-a-repository/configuration-options-for-dependency-updates
https://docs.github.com/en/github/administering-a-repository/keeping-your-actions-up-to-date-with-dependabot