feat: add support for poetry

Poetry will be used for tracking python package dependencies. Utilise
poetry when running scripts. Ensure that the internal CI has access to
to the package.

Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
Change-Id: I3b0991f4fdadc678b50a6bfdce1b374a7e524c2b
diff --git a/group/tf-l1-check-docs/build-docs:nil b/group/tf-l1-check-docs/build-docs:nil
index f86e385..5389df0 100644
--- a/group/tf-l1-check-docs/build-docs:nil
+++ b/group/tf-l1-check-docs/build-docs:nil
@@ -6,6 +6,7 @@
 #
 
 pre_tf_build() {
+	poetry -C "$tf_root" install --with doc
 	targets="doc" set_tf_build_targets
 }