Add sigv4 authentication

[vladimirmukhin]

Sigv4 is a prerequisite for connecting to a Prometheus data source that is managed by AWS
https://docs.aws.amazon.com/prometheus/latest/userguide/AMP-onboard-query-standalone-grafana.html

Upgrade to Grafana 7.3.1 is required since sigv4 is introduced there

[openshift-ci-robot]

Hi @vladimirmukhin. Thanks for your PR.

I'm waiting for a integr8ly member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[HVBE]

/lgtm

verified on upgrade, configuration is propagated to grafana, thanks for contributing @vladimirmukhin 👍

[openshift-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: HubertStefanski

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[HVBE]

also @pb82 FYI, this PR upgrades the base image to 7.3.1