[ terraform-ibm-observability-agents/modules/logs-agent] Include variables to configure agent resources

[fidel-ibm]

Currently the agent doesn't expose a variable to configure the logs-agent resources, although is supported from the logs-agent helm chart

resources:
  limits:
    cpu: 500m
    ephemeral_storage: 10Gi
    memory: 3Gi
  requests:
    cpu: 100m
    ephemeral_storage: 2Gi
    memory: 1Gi

Something like

logs_agent_resources should be sufficient to pass this information, note that the chart enforces the need to pass the entire configuration even if you are changing only one of the values.

[ocofaigh]

PR under review: #470