Use Helm generated instead of cert-manager generated certs for the operator

[jvoravong]

Description:

• Changes for using Helm generated instead of cert-manager generated certs for the operator by default.
• Updated documentation within this repository. The easiest way to view the rendered documents for the 2 main files that matter for this PR is to use these links.
  • https://github.com/signalfx/splunk-otel-collector-chart/blob/otl-2900-migration/UPGRADING.md#01190-to-01200
  • https://github.com/signalfx/splunk-otel-collector-chart/blob/otl-2900-migration/docs/auto-instrumentation-install.md#tls-certificate-requirement-for-kubernetes-operator-webhooks

Testing:

• The added migration steps were tested manually.
• The functional test golden file expected_cluster_receiver.yaml that is used for validation had to be regenerated because by removing cert-manager we removed 3 cert-manager pods that previously generated metrics that were collected.
• Our functional tests also include 2 "upgrade" tests which are expected to fail (due to reasons outlined in UPGRADING.md), thus I had to add the "Ignore Tests" label to this PR. No other tests will be failing except for these upgrading tests, I've linked an instance of these failures for one of the latest commits below.
  • Test helm upgrade in EKS - credentials needed
  • Test helm upgrade from release in EKS - credentials needed
  • I had to add an additional "dummy commit" after the "Ignore Tests" label was applied in order to get CI/CD to pass.

[jinja2]

I think we'll need an entry for how existing certmanager subchart users can keep their current setup in the upgrading guide which we can link to in a changelog entry.

And I think it would be good to document if user can safely disable existing certmanager and use the autogenerate feature when they helm upgrade to a version of chart with this change.

[jvoravong]

Having to use a different PR label to get the upgrade tests to pass, a new PR label can be added after #1682.