Update application env var docs for accuracy

[tcdowney]

This is an initial pass at updating our app env var docs for accuracy. I am planning on submitting a followup PR specific to the 1.2 release to add guidance around how to override the "label" on an UPSI, but that will build upon this one.

• Updates the VCAP_SERVICES docs to clarify managed services are not supported and to only include user-provided services in the example
• Add a note about using the "tags" field instead of "label" when parsing VCAP_SERVICES
• Updates several env var examples to reflect their actual values on Kubernetes

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Please merge to main and cherry-pick this over to the 1.1 and 1.0 release branches.

[cf-gitbot]

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