Feat: Add packer verify Github Actions workflow

Feat: Add packer verify Github Actions workflow

- Update build params with default params to be able to run
  workflows manually.
- Use the default version of packer to v1.9.1.
- Use the latest version v0.4 lfit/checkout-gerrit-change-action
  allow passing the GHA PAT token for all the jobs in the workflow
  file.
- Use base64 encode / decode to handle special characters correctly
  while storing and retriving secrets to/from GHA. Writing secrets
  CLI dependent config files results in an undefined behavior.
- The change requires creating secrets before hand on project with
  secret name as CLOUD_YAML_B64 and CLOUD_ENV_B64 along with the
  $key-value pairs in yaml and hcl format and base64 encoded.

Issue-ID: LF-JIRA RELENG-4761
Change-Id: Ia2989909fe38ed274fc799af747d3ebb218ff3c7
Signed-off-by: Anil Belur <abelur@linuxfoundation.org>