Shorter, more conventional dotdir name than garmin-tokenstores. Restore
the "next to DBPath" join that got dropped when the default was
inlined via getEnvDefault -- an explicit GARMIN_TOKENSTORE still wins
verbatim, but the implicit default must still resolve relative to the
DB file's directory, not the process's CWD.
internal/garmin/client.go's GARMIN_TOKENSTORE env var is now always
set (TokenStorePath can no longer be empty), so the conditional that
only appended it when non-empty is dead code.
Christophe Vila
77f9588c2d