[metachronik, charts.e.cash] Add CMD to end of dockerfile to match pattern of npm deployment dockerfiles, which work

Summary: Use the same node image that works with npm and bash in the npm deployments

Test Plan: proofread, will land and do more testing in CI

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D18404