Cant build snaps with snapcraft when snap store is down

[Bugra Aydogar]

Hi,

As a snap developer, when there is a problem with Snap Store connection, it is not possible to re-build the snaps with `snapcraft` command.

Snapcraft always tries to connect and get/check updates from the store and when the store connection is broken, it blocks all development cycle.

As a workaround, a snap developer could use;
`sudo touch /run/.containerenv`

Although, it could be an expected behaviour to check if there are some updates from the store, in case of connection issues (assuming already have required packages), snapcraft should proceed the operation.

[Sergio Schvezov (sergiusens)]

Scenarios:
- build-snaps
  if the build-snap entries did not change, then noop
- base
  once bootstrapped, no more queries should go on. Manifest generation should use
  our stored values or local queries
- desktop extensions
  can be improved by adding injection logic, no need to refresh if already installed
- if snapcraft and the base are not injected
  don't try to refresh unless the channel has changed (only really applicable
  for snapcraft developers)

[Michał Sawicz (saviq)]

Another scenario are default-providers - Snapcraft checks their validity (bug #2012057), so that will fail.