indra-git: fails to discover repository when project is not at repository root

[cbs228]

The indra-git plugin fails to discover the containing repository if the gradle project does not reside at the repository root. This is not the case for monorepos, git-subtrees, and other repository structures that contain multiple projects.

From IndraGitService.java:115, it appears that the plugin discovers the repository like this:

final Repository repo = new RepositoryBuilder().setWorkTree(targetDir).setGitDir(realGit).setMustExist(true).build();

The upstream JGit documentation recommends using an approach like this:

new RepositoryBuilder()
                .setGitDir(gitDirArgument) // --git-dir if supplied, no-op if null
                .readEnviroment() // scan environment GIT_* variables
                .findGitDir() // scan up the file system tree
                .build()

where findGitDir() traverses up the filesystem like the git executable does.

If indra-git performed a filesystem traversal with findGitDir(), it would probably be compatible with monorepo layouts.