Add env var SPLUNK_CONFIG_YAML for storing configuration YAML

[bjsignalfx]

Supplying Splunk Otel Collector configuration yaml via environment variable SPLUNK_CONFIG_YAML.

One advantage is that this allows for having the config YAML as a parameter value in AWS Systems Manager Parameter Store and thus removing the need to have a volume mounted to a Fargate task to hold the configuration file.

[rmfitzpatrick]

Would you be comfortable setting #450 as the base branch? They will be stepping on each other otherwise.

Also it would be good to document this in places like https://github.com/signalfx/splunk-otel-collector/blob/main/docs/getting-started/linux-manual.md#custom-configuration

[bjsignalfx]

It looks like #450 is ready to be merge. If so, maybe merge then I rebase main? And yes I'll add documentation.

[bjsignalfx]

@rmfitzpatrick So, if SPLUNK_CONFIG and SPLUNK_CONFIG_YAML are specified, which should take precedence? Maybe we should make these mutually exclusive because of equal precedence?

[rmfitzpatrick]

It looks like #450 is ready to be merge. If so, maybe merge then I rebase main? And yes I'll add documentation.

I'm still waiting for a final review and will likely be merging tomorrow if it doesn't come in.

@rmfitzpatrick So, if SPLUNK_CONFIG and SPLUNK_CONFIG_YAML are specified, which should take precedence? Maybe we should make these mutually exclusive because of equal precedence?

I think it makes sense they should be mutually exclusive (w/ --config) always taking priority.

[rmfitzpatrick]

Please add a test in https://github.com/signalfx/splunk-otel-collector/blob/main/tests/general/container_test.go

[tmorrisonsfx]

@bjsignalfx I reviewed the linux-manual.md file. Included a few suggested changes. Thanks!