Added option to scrape all types of attributes

[umutsahin]

Hi @fstab, @tomwilkie

The reason I have created this PR is while scraping JMX metrics from apache ignite, if I used JMXMetricsSpi, exporter was not able to parse any of the metrics provided by specific SPI. The Attributes are returned as POJOs instead of the expectation Attribute implementation.

I have added an option to scrape everything from JMX, current implementation scrapes Attribute instances only. Config key: scrapeAllAttributes

Signed-off-by: Umut Sahin [email protected]

[umutsahin]

Hi @dhoard, is there anything missing from my side to get this PR merged ? Thanks!

[dhoard]

@umutsahin I don't see any JUnit tests for the changes. (I'm working on a robust integration test suite.)