TestData: Support for csv files & csv content (#34674) (#34709)

* initial implementation of csv support for test data source

* CSV file & content scenarios working

* Removing categorical data

* fixing handler names

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Update pkg/tsdb/testdatasource/csv_data.go

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>

* Fixed lint issues

* updated so it uses the same parsing

* more CSV tests

* lint fixes

* more lint

* lint

* support time field

* migrate manual entry to csv

* more test output

* more test output

* missing file

Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>
Co-authored-by: Ryan McKinley <ryantxu@gmail.com>
(cherry picked from commit 987bffe482)

Co-authored-by: Torkel Ödegaard <torkel@grafana.org>

pkg/tsdb/testdatasource/testdata/mixed.csv

@@ -0,0 +1,3 @@
+Field1,Field2,Field3,123
+True,Hello,6,
+False,6,World,6