Remove opamp remote config dir readable validation

[portertech]

The opamp extension configuration was added to sumologic.yaml as part of #1343. The extension is not enabled by default. This initial configuration is intended to aid in the reliability and formatting of setting up remote management via the installation script (install.sh). Unfortunately, the extension validation currently ensures the remote_configuration_directory is readable, causing regular installations to fail, for example:

Dec 12 14:06:40 ip-172-31-27-232 otelcol-sumo[1449]: Error: invalid configuration: extensions::opamp: opamp remote_configuration_directory /etc/otelcol-sumo/opamp.d must be readable: stat /etc/otelcol-sumo/opamp.d: no such file or directory
Dec 12 14:06:40 ip-172-31-27-232 otelcol-sumo[1449]: 2023/12/12 14:06:40 collector server run finished with error: invalid configuration: extensions::opamp: opamp remote_configuration_directory /etc/otelcol-sumo/opamp.d must be readable: stat /etc…such file or directory

This pull-request removes this validation, as the extension does this as part of effective configuration loading, see:

sumologic-otel-collector/pkg/extension/opampextension/opamp_agent.go

Lines 318 to 321 in 6f3f290

	func (o *opampAgent) loadEffectiveConfig(dir string) error {
	if _, err := os.Stat(dir); err != nil {
	return err
	}

We will need to do a release after merging this pull-request (if accepted) in order to fix standard collector installation.

Alternatively, we can remove opamp extension configuration from sumologic.yaml, however, we still need a release and we lose the extra reliability and formatting of setting up remote management via the installation script.

[echlebek]

LGTM 👍

[andrzej-stencel]

Right, I was able to reproduce this issue by running otelcol-sumo v0.89.0-sumo-2 with the following configuration:

exporters:
  logging:
extensions:
  opamp:
    remote_configuration_directory: ./non-existent-dir
receivers:
  hostmetrics:
    scrapers:
      memory:
service:
  pipelines:
    metrics:
      exporters:
        - logging
      receivers:
        - hostmetrics

$ otelcol-sumo-0.89.0-sumo-2-linux_amd64 --config config.yaml
Error: invalid configuration: extensions::opamp: opamp remote_configuration_directory ./non-existent-dir must be readable: stat ./non-existent-dir: no such file or directory
2023/12/13 11:29:48 collector server run finished with error: invalid configuration: extensions::opamp: opamp remote_configuration_directory ./non-existent-dir must be readable: stat ./non-existent-dir: no such file or directory