Replace 'properties/assert' with 'testify/assert'

[nfnt]

What this PR does / why we need it:
This removes the "properties" dependency and uses "testify" instead. The main reason was that the assertions provided by "properties" didn't correctly show the line in which an assertion failed. "testify" does. E.g. "properties" showed assert.go:24: got 1.7.2 want flink app version while "testify" shows

    index_test.go:63: 
        	Error Trace:	index_test.go:63
        	Error:      	Not equal: 
        	            	expected: ""
        	            	actual  : "1.7.2"
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-
        	            	+1.7.2
        	Test:       	TestParseIndexFile
        	Messages:   	flink app version

Also this improves code consistency by removing a package when we have other packages already providing that functionality.

[zen-dog]

🚢