Explicitly install npm in elastic image

[tdmanv]

Change Overview

Should fix the following:

/esdump-setup.sh: line 5: npm: not found
/esdump-setup.sh: line 7: npm: not found
/usr/bin/node
v10.16.3
/esdump-setup.sh: line 13: npm: not found
/esdump-setup.sh: line 14: npm: not found
/esdump-setup.sh: line 15: npm: not found
The command '/bin/sh -c chmod +x /esdump-setup.sh && sync && /esdump-setup.sh' returned a non-zero code: 127
: exit status 127
make[1]: *** [run] Error 1
make: *** [gorelease] Error 2

Pull request type

Please check the type of change your PR introduces:

• 🚧 Work in Progress
• 🌈 Refactoring (no functional changes, no api changes)
• 🐹 Trivial/Minor
• 🐛 Bugfix
• 🌻 Feature
• 🗺️ Documentation
• 🤖 Test

Test Plan

We should test building the image prior to merging.

• 💪 Manual
• ⚡ Unit test
• 💚 E2E