(core): formatAnalytics is documented as supporting plaintext but doesn't

### Describe the bug

https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/core/lib/private/metadata-resource.ts#L65 suggests there's an option to have the analytics format be plaintext rather than compressed. I can't find any other references to `v2:plaintext` in the codebase.

### Expected Behavior

-

### Current Behavior

Docstring doesn't describe code

### Reproduction Steps

-

### Possible Solution

I'm unsure if the code is wrong or if the docstring is wrong, someone who knows the project better than me would have to make that call.

### Additional Information/Context

I found this while trying to debug an issue with the metadata "flipping" back and forward on the same code from two different developers. Plaintext would be really helpful here since a deflate64 string is basically useless in `cdk diff`

### CDK CLI Version

2.113.0 (build ccd534a)

### Framework Version

_No response_

### Node.js Version

v18.17.1

### OS

Windows 11

### Language

TypeScript

### Language Version

_No response_

### Other information

_No response_

Read packages/aws-cdk-lib/core/lib/private/metadata-resource.ts around line 65, then search the codebase for formatAnalytics and v2:plaintext. Determine whether the implementation or docstring is authoritative; done means the documented option and actual behavior agree, with the relevant behavior covered by an appropriate test if one exists.

Written by the indexing model from the issue text.