GOBBLIN-2184. Disable releases for apache.snapshots repo

[adoroszlai]

What changes were proposed in this pull request?

The Apache snapshot repository should be enabled only for snapshots.

https://issues.apache.org/jira/browse/GOBBLIN-2184

How was this patch tested?

Local build:

$ ./gradlew compileJava
...
BUILD SUCCESSFUL in 3m 1s
209 actionable tasks: 209 executed

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 48.51%. Comparing base (003590e) to head (6ee3b90).
Report is 4 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #4088      +/-   ##
============================================
+ Coverage     47.98%   48.51%   +0.53%     
- Complexity     8373     9156     +783     
============================================
  Files          1582     1775     +193     
  Lines         62712    68138    +5426     
  Branches       7105     7312     +207     
============================================
+ Hits          30091    33057    +2966     
- Misses        29899    32293    +2394     
- Partials       2722     2788      +66     

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[adoroszlai]

@phet could you please help review this?