feat(bkgpslog):Include more fields in VERSION

These fields are included to automatically-generated VERSION file
included when a new tar is generated or the script is restarted:

- SCRIPT_VERSION  : Version of bkgpslog being run.
- SCRIPT_NAME     : Name of the script being run ("bkgpslog").
- SCRIPT_URL      : URL where script can be downloaded.
- AGE_VERSION     : Version of age (encryption program) used.
- AGE_URL         : URL where age can be downloaded.
- DATE            : Creation timestamp (ISO-8601).
- HOSTNAME        : Hostname of device running script.
- PUBKEY_[n]      : Pubkey string used by age to encrypt.