feat: Publish charms and snaps to branch on pull request

[markbeierl]

This change will push to a branch under edge with the same name as the branch on which the job runs.

For example, a PR using a branch called TELCO-1082-Publish-charms-and-snaps-to-branch-on-pull-request would look like the following after a successful run:

charmcraft status sdcore-upf-k8s
Track    Base                  Channel                                                             Version    Revision    Resources                                  Expires at                                                      
latest   ubuntu 22.04 (amd64)  stable                                                              -          -           -                                                                                                          
                               candidate                                                           -          -           -                                                                                                          
                               beta                                                                13         13          bessd-image (r5), pfcp-agent-image (r5)                                                                    
                               edge                                                                21         21          bessd-image (r8), pfcp-agent-image (r7)                                                                    
1.3      ubuntu 22.04 (amd64)  stable                                                              -          -           -                                                                                                          
                               candidate                                                           -          -           -                                                                                                          
                               beta                                                                13         13          bessd-image (r5), pfcp-agent-image (r5)                                                                    
                               edge                                                                70         70          bessd-image (r16), pfcp-agent-image (r14)                                                                  
                               edge/TELCO-1082-Publish-charms-and-snaps-to-branch-on-pull-request  72         72          bessd-image (r16), pfcp-agent-image (r14)  2024-04-19T00:00:00Z                                            

Note that the developer must either log into the store or know the name of the branch explicitly in order to use it.