[prometheus-thanos] Add parameter to create service accounts

[aperigault]

What this PR does / why we need it:

To use Web Identity providers for IAM credentials for AWS EKS we need a kubrnetes service account with specific annotation. This PR add a service account for each thanos component with an annotation option.

Related thanos fixed issue: https://github.com/thanos-io/thanos/issues/1494

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• [X] DCO signed
• [X] Chart Version bumped (if the pr is an update to an existing chart)
• [X] Variables are documented in the README.md
• [X] Title of the PR starts with chart name (e.g. [fluentd-elasticsearch])