Apply korro to samples in data sources

[Allex-Nik]

Adds usage of korro to the samples in the following webpages:

• https://kotlin.github.io/dataframe/data-sources.html - and all subpages
• https://kotlin.github.io/dataframe/readsqldatabases.html
• https://kotlin.github.io/dataframe/read.html

Related to #987, but does not change https://kotlinlang.org/docs/data-analysis-connect-to-db.html (as it will be done separately later). In addition, https://kotlin.github.io/dataframe/readsqlfromcustomdatabase.html was already done by @Jolanrensen

[Allex-Nik]

Is the package correct for the samples? Should ReadSQLDatabases be in api instead of io?

[Allex-Nik]

I added the import and applied korro, so some samples below were changed by the functions in Parquet.kt that had already existed

[koperagen]

Maybe worth to turn code snipper with text above into

val text = """[
{
"A": "1",
"B": 1,
"C": 1.0,
"D": true
},
{
"A": "2",
"B": 2,
"C": 1.1,
"D": null
},
{
"A": "3",
"B": 3,
"C": 1,
"D": false
},
{
"A": "4",
"B": 4,
"C": 1.3,
"D": true
}
]
"""
val df = DataFrame.readJsonStr(text)

[Allex-Nik]

Done

[koperagen]

Tables in Manage type clashes and Column type inference from CSV could be replaced with iframes

[Allex-Nik]

Tables in Manage type clashes and Column type inference from CSV could be replaced with iframes

I have done it in these sections (and in some others for consistency) and also added iframes for the results where it seemed useful