fix discovery and OpenAPI generation

[tangiel]

• Methods with absolute paths should now generate the correct discovery output. The common path prefix builder is used to compute the service path and basepath using methods' canonical paths (including API name and version). A method with a path of /notinanyapipath will result in a blank service path and a base URL of the Endpoints root path.
• Resources that are shared across multiple APIs now correctly have their field schema added to the API as well.

[tangiel]

@clementdenis this should fix the discovery path issue

[codecov-io]

Codecov Report

Merging #53 into master will increase coverage by 0.08%.

@@             Coverage Diff              @@
##             master      #53      +/-   ##
============================================
+ Coverage     79.66%   79.74%   +0.08%     
- Complexity     1608     1617       +9     
============================================
  Files           153      153              
  Lines          5415     5427      +12     
  Branches        694      698       +4     
============================================
+ Hits           4314     4328      +14     
  Misses          829      829              
+ Partials        272      270       -2

Impacted Files	Coverage Δ	Complexity Δ
.../api/server/spi/config/model/SchemaRepository.java	94.79% <100%> (+0.47%)	28 <5> (+5)	:white_check_mark:
...oogle/api/server/spi/swagger/SwaggerGenerator.java	76.55% <100%> (ø)	51 <10> (ø)	:x:
...e/api/server/spi/discovery/DiscoveryGenerator.java	87.62% <100%> (+0.43%)	51 <10> (+1)	:white_check_mark:
...e/api/server/spi/config/model/ApiMethodConfig.java	87.42% <100%> (+0.38%)	67 <1> (+2)	:white_check_mark:
.../server/spi/discovery/CommonPathPrefixBuilder.java	100% <ø> (+5.55%)	9% <ø> (+1%)	:white_check_mark:

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