Review version tagging on make install

`make install` uses `git describe --exact-match --tags` to find the version of elastic-package. This is error prone because it depends on the status of the working copy and its remotes.

We should try to find a more reliable mechanism.

Start by inspecting the make install target and its current git describe --exact-match --tags invocation. Trace how the version is used during installation, then determine a reliable source that does not depend on the working copy or remotes; done means make install reports and installs the intended version consistently.

Written by the indexing model from the issue text.