Generalizing BWC building so that there is less code to modify for a release. This ensures we do not
need to think about what major or minor version is in the gradle code. It follows the general rules of the
elastic release structure. For more information on the rules, see the VersionCollection's javadoc.
This also removes the additional bwc snapshots that will never be released, such as 6.0.2, which were
being built and tested against every time we ran bwc tests.
Additionally, it creates 4 new projects that correspond to the different types of snapshots that may exist
for a given version. Its possible to now run those individual tasks to work out bwc logic whereas
previously it was impossible and the entire suite of bwc tests had to be run to work out any logic
changes in the build tools' bwc project. Please note that if the project does not make sense for the
version that is current, that an error will be thrown from that individual project if an attempt is made to
run it.
This should allow for automating the version bumps as well, since it removes all the hardcoded version
logic from the configs.
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