Replace LocalObjectReference usage with strings in exp/etcdrestore API

[furkatgofurov7]

What this PR does / why we need it:
Additionally, currently when running make build-chart & release-chart Makefile targets throw:

/Users/userX/repos/rancher-turtles/hack/tools/bin/helm-v3.15.3 package out/charts/rancher-turtles --app-version=est/v0.11.0 --version=est/v0.11.0 --destination=out/package
Error: Invalid Semantic Version
make: *** [build-chart] Error 1

error and that is because of how we construct HELM_CHART_TAG variable. In this patch, the extraction command was updated to use grep with a regular expression to ensure it extracts a valid semantic version (e.g., v0.11.0) and both helm package commands run as expected.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #729

Special notes for your reviewer:

Checklist:

• squashed commits into logical changes
• includes documentation
• adds unit tests
• adds or updates e2e tests

[Danil-Grigorev]

Thanks!