The script now uses the path of the script file itself to determine the
manifests directory paths. This fixes an issue when building the AUR
packages where the check() phase would fail because the git repository
of the package would be used and this would generate invalid paths.

Signed-off-by: Aurel Canciu <aurelcanciu@gmail.com>

There was an assumption in this script that it is always executed in Git
repository/directory, this is however not always true, for example when
one downloads the `.tar.gz` that is made available for every release
by GitHub (and used in one of our AUR packages).

This commit changes this, and makes the first argument of `bundle.sh`
configurable, so a custom manifests directory can always be defined
_without_ relying on Git.

Omitting it, or passing an empty string, will still fall back to the
previous behavior of using `git rev-parse --show-toplevel`.

Signed-off-by: Hidde Beydals <hello@hidde.co>

- add make target for generating the install manifests using kustomize
- embed the generated manifests in flux binary
- the install and bootstrap commands default to using the embedded manifests
- download the install manifests from GitHub only if the install/bootstrap version arg is set

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>