Respect fleet spec when provisioning on run apply

[r4victor]

Closes #2969

This PR implements functions for combining fleet and run profiles and requirements so that process_submitted_jobs respects both fleet and run specs when provisioning new instances. If fleet spec and run spec are not compatible / have empty intersection – job is terminated with FAILED_TO_START_DUE_TO_NO_CAPACITY. Run plan offers are not affected by this PR and do not respect fleet spec – to keep dstack offers logic intact and because run plan offers will be different for different fleets. We may introduce per-fleet offers in run plan after #3021 and #3020.

Example: respect fleet backend

type: fleet
name: cloud-fleet
placement: any
nodes: 0..2
backends:
  - runpod

type: dev-environment
ide: vscode
fleets:
  - cloud-fleet

✗ dstack apply
 Project              main                           
 User                 admin                          
 Configuration        .dstack.yml                    
 Type                 dev-environment                
 Resources            cpu=2.. mem=8GB.. disk=100GB.. 
 Spot policy          auto                           
 Max price            -                              
 Retry policy         -                              
 Creation policy      reuse-or-create                
 Idle duration        5m                             
 Max duration         -                              
 Inactivity duration  -                              
 Reservation          -                              

 #  BACKEND           RESOURCES                           INSTANCE TYPE     PRICE     
 1  gcp               cpu=2 mem=8GB disk=100GB (spot)     e2-standard-2     $0.0295   
    (europe-west4)                                                                    
 2  gcp               cpu=2 mem=8GB disk=100GB (spot)     n4-standard-2     $0.0316   
    (europe-west4)                                                                    
 3  gcp               cpu=2 mem=8GB disk=100GB (spot)     n2-standard-2     $0.0354   
    (europe-west4)                                                                    
    ...                                                                               
 Shown 3 of 2237 offers, $56.62656max

Submit a new run? [y/n]: y
⠧ Launching cowardly-dog-1...
 NAME              BACKEND          RESOURCES                 PRICE    STATUS  SUBMI… 
 cowardly-dog-1    runpod (FR)      cpu=8 mem=30GB            $0.11    provi…  50 se… 
                                    disk=100GB                                        
                                    RTX3090:24GB:1 (spot)