Fix default prometheus datasource was not found error

[mobeigi]

Proposed changes

When using this Grafana dashboard, we get the following error: Datasource named ${DS_PROMETHEUS} was not found. This change fixes this issue.

Checklist

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• [ X ] I have read the CONTRIBUTING guide
• [ X ] I have proven my fix is effective or that my feature works
• [ X ] I have checked that all unit tests pass after adding my changes
• [ X ] I have ensured the README is up to date
• [ X ] I have rebased my branch onto master
• [ X ] I will ensure my PR is targeting the master branch and pulling from my branch on my own fork

[Rulox]

Thanks @mobeigi

We'll have a look at this ASAP and get back to you

[Rulox]

Thanks, I've had a look, it seems is a common error that happens when this is not defined. Same error in other repos is fixed in the same way:

https://github.com/kubernetes/ingress-nginx/pull/4797/files

I've tested it and it looks good to me.

Once you get 2 approvals, could you squash your 2 commits into one?, After that I'll make sure to merge it. Thanks

[mobeigi]

@Rulox Squashed the commits 😄

[Dean-Coakley]

@mobeigi Thanks a lot for this fix!