Build client with passing the version and revision

[nkuba]

The client expects version and revision to be provided on build with -ldflags.

Here we use the git commands to obtain the values.

version

Will be set to the latest tag on the branch, so when we checked out a tag it will be set to the tag name, e.g. v1.3.1. But if the current HEAD is not a tag it will produce a uniqe value based on the latest tag, number of commits since the tag, and commit hash, e.g. v1.3.1-5816-g8219ddcf9.

Read more: https://git-scm.com/docs/git-describe

revision

Revision will be set simply to a short version of the HEAD commit hash. Read more: https://git-scm.com/docs/git-rev-parse

make build command

The make build command will default to the version and revision values described above. However the values can be overwritten when calling the command by simply appending the arguments: make build version=2.0.0 or make build version=2.0.0-dev revision=rev-123.