The GCP host searches for application default credentials in known
locations within the user's home directory using
`seastar::file_exists()`. However, this function does not perform tilde
expansion in pathnames.
Replace tildes with the home directory from the HOME environment
variable.
Signed-off-by: Nikos Dragazis <nikolaos.dragazis@scylladb.com>
(cherry picked from commit 77cc6a7bad)