VAULT-5280 add telemetry annotations for agent sidecar

[kschoche]

• Adds a new annotation for vault.hashicorp.com/agent-telemetry which defines the telemetry configuration for the agent sidecar. All parameters linked above are currently supported.
• The annotation behaves similarly to vault.hashicorp.com/auth-config in that you specify an annotation via vault.hashicorp.com/agent-telemetry-<key>: "<value>"

An example which configures prometheus telemetry on the agent sidecar for an application:

annotations:
	"vault.hashicorp.com/agent-telemetry-prometheus_retention_time": "30s",
	"vault.hashicorp.com/agent-telemetry-disable_hostname":          "true",

..which results in the following configuration stanza being added to the sidecar environment via rendering the environment:

telemetry {
  prometheus_retention_time = "30s"
  disable_hostname = true
}

Note to Reviewers: docs PR hashicorp/vault#18681

[swenson]

LGTM

[benashz]

Looking good! I only had one suggestion for the tests.

[benashz]

Just a few minor nits to address, then 👍