refactor: move LAVA job definition templates into independent files

This change introduces a new script function to expand the variables in
a file. With this, we can move the LAVA YAML job template descriptions,
which are currently embedded inside individual HEREDOCs, into their own
files.

Signed-off-by: Chris Kay <chris.kay@arm.com>
Change-Id: I09805ab4b6894a371e63a944d113ca2f475a806b
15 files changed