Add build and test GH action, fix TestGetApps race condition (#83)

[jgwest]

This PR:

• Adds a GitHub action to the workflow that runs the build (both docker and standalone), and then runs go test (the job/steps are based on Argo CD's)
• Fixes the TestGetApps test, which was intermittently failing due to string ordering

Failing test:

2020/11/24 12:08:52 proto: tag has too few fields: "-"
--- FAIL: TestGetApps (0.00s)
    --- FAIL: TestGetApps/Happy_Flow (0.00s)
        repo_service_test.go:156: 
            	Error Trace:	repo_service_test.go:156
            	Error:      	Not equal: 
            	            	expected: []string{"app2", "app1"}
            	            	actual  : []string{"app1", "app2"}
            	            	
            	            	Diff:
            	            	--- Expected
            	            	+++ Actual
            	            	@@ -1,4 +1,4 @@
            	            	 ([]string) (len=2) {
            	            	- (string) (len=4) "app2",
            	            	- (string) (len=4) "app1"
            	            	+ (string) (len=4) "app1",
            	            	+ (string) (len=4) "app2"
            	            	 }
            	Test:       	TestGetApps/Happy_Flow
FAIL

[jgwest]

Review comments addressed and PR rebased.

[wtam2018]

/LGTM