feat: custom branch name templates (#571)

* Add branch-name-template config option

* Logging

* Use branch name template

* Add label to template variables

* Add description template variable

* More concise description for branch_name_template

* Remove more granular time template variables

* Only fetch first label

* Add check for empty template-generated name

* Clean up comments, docstrings

* Merge createBranchTemplateVariables into generateBranchName

* Still replace undefined values

* Fall back to default on duplicate branch

* Parameterize description wordcount

* Remove some over-explanatory comments

* NUM_DESCRIPTION_WORDS: 3 -> 5

src/github/types.ts

@@ -63,6 +63,11 @@ export type GitHubPullRequest = {
   additions: number;
   deletions: number;
   state: string;
+  labels: {
+    nodes: Array<{
+      name: string;
+    }>;
+  };
   commits: {
     totalCount: number;
     nodes: Array<{
@@ -88,6 +93,11 @@ export type GitHubIssue = {
   updatedAt?: string;
   lastEditedAt?: string;
   state: string;
+  labels: {
+    nodes: Array<{
+      name: string;
+    }>;
+  };
   comments: {
     nodes: GitHubComment[];
   };