Install github dco app for use in ci-config-travis and ci-config-github-actions repos

[mhdawson]

For the new ci-config repos requested by the Package-maintenance team I'd like to enable the DCO github app https://github.com/apps/dco to enforce sign offs for the commits.

[mcollina]

sgtm

[mhdawson]

Discussed in TSC meeting 16 April 2020 and agreed could proceed if no objections in 72 hours: https://github.com/nodejs/TSC/blob/master/meetings/2020-04-16.md#nodejsadmin

[mhdawson]

It requires these permissions:

Read access to code
Read access to members, metadata, and pull requests
Read and write access to checks

Will install for only the 2 specified repositories.

[joesepi]

SGTM

[bnb]

+1, happy to enable projects to leverage apps they need.

[BethGriggs]

+1

[mhdawson]

Installed for the 2 specific repositories.