Split ENABLE_LEGACY_PROVIDER_JOBS into independent FTP/HARMONIE flags

Real LVGMC FTP credentials arrived today; real DMI HARMONIE
credentials haven't. The combined flag would have enabled both the
moment FTP's were ready, crash-looping the app on HARMONIE's still-
placeholder values via parMapN — caught this before it happened
(the Grib job was ~15 min from its first scheduled run). Split into
ENABLE_LVGMC_FTP_JOBS and ENABLE_HARMONIE_JOBS so each provider can
be enabled independently as its own credentials become real.

.env-sample

@@ -6,11 +6,13 @@ POSTGRES_HOST=postgres
 APP_BIND_ADDRESS=127.0.0.1
 APP_PORT=9090
 ENABLE_SCHEDULED_JOBS=true
-# Gates the FTP station fetch and DMI Harmonie fetch specifically, separately
-# from ENABLE_SCHEDULED_JOBS, since both require real credentials below.
-# Leave false until those are real; both jobs throw on placeholder values,
+# Gate the FTP station fetch and DMI Harmonie fetch independently, separately
+# from ENABLE_SCHEDULED_JOBS, since each requires its own real credentials
+# below and they tend to arrive on different timelines. Leave false until a
+# given one's credentials are real; each job throws on placeholder values,
 # and would otherwise crash-loop the whole app rather than just fail quietly.
-ENABLE_LEGACY_PROVIDER_JOBS=false
+ENABLE_LVGMC_FTP_JOBS=false
+ENABLE_HARMONIE_JOBS=false
 
 LVGMC_URL=aaa
 LVGMC_USER=aaa