feat(17-02): add gocron dependency, subscribers and scheduled_jobs tables with CRUD

- Add gocron/v2 v2.19.1 as direct dependency
- Append subscribers and scheduled_jobs CREATE TABLE to schema.sql
- Implement full subscriber CRUD (Add/Remove/List/IsSubscribed)
- Implement full scheduled job CRUD (Save/List/Get/Delete/UpdateLastRun/SetEnabled)

go.mod

@@ -35,6 +35,7 @@ require (
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/emirpasic/gods v1.18.1 // indirect
 	github.com/fsnotify/fsnotify v1.9.0 // indirect
+	github.com/go-co-op/gocron/v2 v2.19.1 // indirect
 	github.com/go-git/gcfg v1.5.1-0.20230307220236-3a3c6141e376 // indirect
 	github.com/go-git/go-billy/v5 v5.8.0 // indirect
 	github.com/go-viper/mapstructure/v2 v2.4.0 // indirect
@@ -42,6 +43,7 @@ require (
 	github.com/google/uuid v1.6.0 // indirect
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/jbenet/go-context v0.0.0-20150711004518-d14ea06fba99 // indirect
+	github.com/jonboulle/clockwork v0.5.0 // indirect
 	github.com/kevinburke/ssh_config v1.2.0 // indirect
 	github.com/lucasb-eyer/go-colorful v1.2.0 // indirect
 	github.com/mattn/go-runewidth v0.0.16 // indirect
@@ -52,6 +54,7 @@ require (
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
+	github.com/robfig/cron/v3 v3.0.1 // indirect
 	github.com/sagikazarmark/locafero v0.11.0 // indirect
 	github.com/sergi/go-diff v1.3.2-0.20230802210424-5b0b94c5c0d3 // indirect
 	github.com/skeema/knownhosts v1.3.1 // indirect