fix(cairo): load text_loader.json as a file if cannot be found as a resource

[glasstiger]

QuestDB doc says that a custom version of text_loader.json can be loaded from the conf directory if the below property is set:

cairo.sql.copy.formats.file=text_loader_custom.json

This did not work.
The PR fixes the issue by falling back to loading the file from the conf dir if it cannot be found as a resource.

Closes #1928

[ideoma]

[PR Coverage check]

😍 pass : 18 / 25 (72.00%)

file detail

	path	covered line	new line	coverage
🔵	io/questdb/cutlass/text/types/InputFormatConfiguration.java	11	18	61.11%
🔵	io/questdb/PropServerConfiguration.java	1	1	100.00%
🔵	io/questdb/cutlass/text/DefaultTextConfiguration.java	5	5	100.00%
🔵	io/questdb/cairo/DefaultCairoConfiguration.java	1	1	100.00%