(SUP-2137) To add parameters to configure telegraf database retention policy

[henrywangpuppet]

Updated in latest comments

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puppet_metrics_dashboard is a class

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puppet_metrics_dashboard::post_start_configs is a class

that may have no external impact to Forge modules.

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[henrywangpuppet]

Update coding to make it simpler, in general, this PR:
Add a new parameter Optional[String[1]] $telegraf_db_retention_duration = undef,
Once set up a value, for example 6w, the puppet agent run will setup a retention policy for the database telegraf is using:

[root@pe-201981-agent-2 log]# puppet agent -t
Info: Using configured environment 'production'
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Retrieving locales
Info: Loading facts
Info: Caching catalog for pe-201981-agent-2.puppetdebug.vlan
Info: Applying configuration version '1632987795'
Notice: /Stage[main]/Puppet_metrics_dashboard::Post_start_configs/Exec[create default telegraf database retention policy]/returns: executed successfully
Notice: Applied catalog in 0.50 seconds
[root@pe-201981-agent-2 log]#

In the corresponding database, a retention policy telegraf_default is added with the duration specified:

> show retention policies on telegraf;
name             duration  shardGroupDuration replicaN default
----             --------  ------------------ -------- -------
autogen          0s        168h0m0s           1        false
telegraf_default 1008h0m0s 24h0m0s            1        true

Resetting the parameter to undef will remove the policy:

[root@pe-201981-agent-2 log]# puppet agent -t
Info: Using configured environment 'production'
Info: Retrieving pluginfacts
Info: Retrieving plugin
Info: Retrieving locales
Info: Loading facts
Info: Caching catalog for pe-201981-agent-2.puppetdebug.vlan
Info: Applying configuration version '1632987795'
Notice: /Stage[main]/Puppet_metrics_dashboard::Post_start_configs/Exec[drop existing retention policy if ever created]/returns: executed successfully
Notice: Applied catalog in 0.51 seconds

> show retention policies on telegraf;
name    duration shardGroupDuration replicaN default
----    -------- ------------------ -------- -------
autogen 0s       168h0m0s           1        false

Lab implemented this pr:

PE 10.32.47.152 - Node Group: MetricsDashboardTest-2
Dashboard: 10.32.47.92

[coreymbe]

Finished testing these changes out late last week. Everything LGTM!