Closes#5069 back-end part
And:
- do not display schemaPendingUpdates status on remote server lists as
this call will become too costly if there are dozens of servers
- (refacto) create foreignTableService
After this is merged we will be able to delete remoteTable's
availableTables column
## Context
#4774
## How was it tested
Locally
## In further PRs
- Update connection status upon page change
- Adapt Info banner to dark mode
- placeholders for form