[messaging] remove v2 feature flag (#4845)

## Context
We are now removing Messaging V2 feature flag to use it everywhere.

## Implementation
- renaming FetchWorkspaceMessagesCommandsModule to
MessagingCommandModule to make it more generic since it it hosts all
commands related to the messaging module
- creating a crons folder inside commands and jobs crons should be named
with xxx.cron.command.ts instead of xxx.command.ts. Same for jobs, jobs
should be named with xxx.cron.job.ts. In a future PR we should make sure
those CronJobs implement a CronJob interface since it's a bit different
(a CronJob does not contain a payload compared to a Job)
- Cron commands have been renamed to "cron:$module:command" so
`fetch-all-workspaces-messages-from-cache:cron:start` has been renamed
to `cron:messaging:gmail-fetch-messages-from-cache`. Also having to
create a command to stop the cron is a bit painful to maintain so I
removed them for now, this can be easily done manually with pg-boss or
bull-mq
- Removing full-sync and partial-sync commands as they were there for
testing only, we might put them back at some point but we will have to
adapt the code anyway.
- Feature flag has been removed from the MessageChannel standard object
to make sure those new columns are created during the next sync-metadata

packages/twenty-server/src/engine/core-modules/feature-flag/feature-flag.entity.ts

@@ -19,7 +19,6 @@ export enum FeatureFlagKeys {
   IsEventObjectEnabled = 'IS_EVENT_OBJECT_ENABLED',
   IsAirtableIntegrationEnabled = 'IS_AIRTABLE_INTEGRATION_ENABLED',
   IsPostgreSQLIntegrationEnabled = 'IS_POSTGRESQL_INTEGRATION_ENABLED',
-  IsFullSyncV2Enabled = 'IS_FULL_SYNC_V2_ENABLED',
   IsMultiSelectEnabled = 'IS_MULTI_SELECT_ENABLED',
 }