Make the clusterName value optional in EKS and GKE

[crobert-1]

Description:

Now that the resource detection processor supports detecting the k8s.cluster.name in GKE and EKS environments, the clusterName value can be optional in these environments.

A simplified resource detection processor has been added to more pipelines in this change as well, in every place the clusterName was manually being added.

Testing:
Tested in GKE and kOps. GKE sets cluster name properly without it specified, and overrides the detected k8s.cluster.name when clusterName is set. kOps fails without clusterName with the following message:

crobert$ ~/dev/splunk-otel-collector-chart $ helm upgrade ...
Error: UPGRADE FAILED: values don't meet the specifications of the schema(s) in the following chart(s):
splunk-otel-collector:
- (root): Must validate "then" as "if" was valid
- clusterName: String length must be greater than or equal to 1
- (root): Must validate all the schemas (allOf)

The - (root) lines are a bit confusing, but that's simply saying that the check failed, AFAICT.

Documentation:
Updated README and relevant comments in code.

[jvoravong]

To get the EKS functional-tests up and running, you will have to close this PR and open up a different PR in a specific way due to recent project test updates. The EKS functional tests need to run with credentials that are only available in this repo.

• Create your feature branch in the https://github.com/signalfx/splunk-otel-collector-chart repo and not your personal fork.
• Create the PR with the feature branch in the https://github.com/signalfx/splunk-otel-collector-chart repo against the main branch.

[jvoravong]

These changes LGTM. A couple small nits. Will approve a separate PR that has the EKS functional tests passing.

[atoulme]

Indeed, please push to this repository and open a PR rather than from your fork.

[crobert-1]

Closing in favor of #1067