[FLINK-31735][docs] Document 'plan' field as object

[zentol]

Fixes an issue where plan field of the JobDetailsInfo was documented as a string, when in fact we write the json plan as a raw object.

[flinkbot]

CI report:

• 53ab76e Azure: SUCCESS

Bot commands

The @flinkbot bot supports the following commands:

• @flinkbot run azure re-run the last Azure build

[dmvk]

in the open api spec, we have

    RawJson:
      type: object

is that actually correct? If I understand it correctly we should be able to pass anything in the rawjson, for example "string"

[dmvk]

nvm, it's correct, it just doesn't align with the HTML docs

[zentol]

If I understand it correctly we should be able to pass anything in the rawjson, for example "string"

Technically you are correct, but we only use RawJson for objects. Should this change the docs will be wrong again.

There isn't much of a point in using this for other data types though, so I'm not worried.

[dmvk]

LGTM 👍 Great stuff!