(SUP-3201) Make Grafana datasource idempotent

[m0dular]

Prior to this commit, using the grafana_datasource resource with "secure
json" parameters was not idempotent. This is because the api obfuscates
these values, so we can't check the state of the datasource using this
resource.

This commit uses the "provisioning" directory to set the datasource at
service startup. It uses a template to create the file so the token can
be a Sensitive type and be redacted from logs and reports.

It also adds an exec to make sure Grafana is ready to accept
connections.

[puppet-community-rangefinder]

puppet_operational_dashboards is a class

that may have no external impact to Forge modules.

puppet_operational_dashboards::profile::dashboards is a class

that may have no external impact to Forge modules.

puppet_operational_dashboards::telegraf::agent is a class

that may have no external impact to Forge modules.

This module is declared in 0 of 579 indexed public Puppetfiles.

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These results were generated with Rangefinder, a tool that helps predict the downstream impact of breaking changes to elements used in Puppet modules. You can run this on the command line to get a full report.

Exact matches are those that we can positively identify via namespace and the declaring modules' metadata. Non-namespaced items, such as Puppet 3.x functions, will always be reported as near matches only.