chore: add Gradle features for sspi and osgi

[vlsi]

That results in optional=true in the published pom.xml.

We do not publish Gradle Metadata yet as it is not trivial
to publish shadowed jar under default coordinate and generate
metadata for it.

closes #1795

--

The resulting pom becomes

  <dependencies>
    <dependency>
      <groupId>com.github.waffle</groupId>
      <artifactId>waffle-jna</artifactId>
      <version>1.9.1</version>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>org.osgi</groupId>
      <artifactId>org.osgi.core</artifactId>
      <version>4.3.1</version>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>org.osgi</groupId>
      <artifactId>org.osgi.enterprise</artifactId>
      <version>4.2.0</version>
      <optional>true</optional>
    </dependency>
  </dependencies>

[codecov-commenter]

Codecov Report

Merging #1797 into master will increase coverage by 0.08%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #1797      +/-   ##
============================================
+ Coverage     69.18%   69.27%   +0.08%     
- Complexity     4206     4212       +6     
============================================
  Files           191      191              
  Lines         17345    17345              
  Branches       2863     2863              
============================================
+ Hits          12000    12015      +15     
+ Misses         4047     4037      -10     
+ Partials       1298     1293       -5     

[ecki]

Would it make sense to add a test for OSGi headers and their optional attributes?

[vlsi]

There's a half-baked OSGi test for it: #507

The last I remember is OSGi server turned out debug logs at Travis for an unknown reasons, which resulted in too much logging and Travis marking the job as erroneous.

[vlsi]

@ecki , do you think you could pick it up and make it work?

Frankly speaking, I do not have lots of OSGi experience.

[ecki]

For The specific case I guess some asserts on the jar manifest would be a good start, i will have a look.