Issue title: [prometheus-snmp-exporter] how to update snmp.yaml through secret
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Describe *in detail* the feature/behavior/change you'd like to see.
1. I am trying to update the snmp configurations through a secret. I could do that through a configmap but nit by secret
2. Is there any way to only put credentials through secret or entire snmp.yaml by a secret.
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**Is your feature request related to a problem? Please describe.**
1. I am trying to update the snmp configurations through a secret. I could do that through a configmap but not by secret
2. Is there any way to only put credentials through secret or entire snmp.yaml by a secret.
I created a secret as mentioned on additional secret but no luck

**Describe the solution you'd like**
snmp.yaml config through secret

**Describe alternatives you've considered**
A clear and concise description of any alternative solutions or features you've considered.

**Additional context**
Add any other context or screenshots about the feature request here.

 Comments: 
 Comment 0: This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Any further update will cause the issue/pull request to no longer be considered stale. Thank you for your contributions.

 Comment 1: This issue is being automatically closed due to inactivity.

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