Major Description
csv writer actually has an implicit limit on column name length due to univocity-parser,
when we initialize a writer https://github.com/uniVocity/univocity-parsers/blob/e09114c6879fa6c2c15e7365abc02cda3e193ff7/src/main/java/com/univocity/parsers/common/AbstractWriter.java#L211, it calls toIdentifierGroupArray which calls valueOf in NormalizedString.java eventually (https://github.com/uniVocity/univocity-parsers/blob/e09114c6879fa6c2c15e7365abc02cda3e193ff7/src/main/java/com/univocity/parsers/common/NormalizedString.java#L205-L209)
in that stringCache.get, it has a maxStringLength cap https://github.com/uniVocity/univocity-parsers/blob/e09114c6879fa6c2c15e7365abc02cda3e193ff7/src/main/java/com/univocity/parsers/common/StringCache.java#L104 which is 1024 by default
we do not expose this as configurable option, leading to NPE when we have a column name larger than 1024,
```
[info] Cause: java.lang.NullPointerException:
[info] at com.univocity.parsers.common.AbstractWriter.submitRow(AbstractWriter.java:349)
[info] at com.univocity.parsers.common.AbstractWriter.writeHeaders(AbstractWriter.java:444)
[info] at com.univocity.parsers.common.AbstractWriter.writeHeaders(AbstractWriter.java:410)
[info] at org.apache.spark.sql.catalyst.csv.UnivocityGenerator.writeHeaders(UnivocityGenerator.scala:87)
[info] at org.apache.spark.sql.execution.datasources.csv.CsvOutputWriter$.writeHeaders(CsvOutputWriter.scala:58)
[info] at org.apache.spark.sql.execution.datasources.csv.CsvOutputWriter.<init>(CsvOutputWriter.scala:44)
[info] at org.apache.spark.sql.execution.datasources.csv.CSVFileFormat$$anon$1.newInstance(CSVFileFormat.scala:86)
[info] at org.apache.spark.sql.execution.datasources.SingleDirectoryDataWriter.newOutputWriter(FileFormatDataWriter.scala:126)
[info] at org.apache.spark.sql.execution.datasources.SingleDirectoryDataWriter.<init>(FileFormatDataWriter.scala:111)
[info] at org.apache.spark.sql.execution.datasources.FileFormatWriter$.executeTask(FileFormatWriter.scala:269)
[info] at org.apache.spark.sql.execution.datasources.FileFormatWriter$.$anonfun$write$15(FileFormatWriter.scala:210)
```
it could be reproduced by a simple unit test
```
val row1 = Row("a")
val superLongHeader = (0 until 1025).map(_ => "c").mkString("")
val df = Seq(s"${row1.getString(0)}").toDF(superLongHeader)
df.repartition(1)
.write
.option("header", "true")
.option("maxColumnNameLength", 1025)
.csv(dataPath)
```
