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

test/data-formatter.test.ts

@@ -28,6 +28,9 @@ describe("formatContext", () => {
       additions: 50,
       deletions: 30,
       state: "OPEN",
+      labels: {
+        nodes: [],
+      },
       commits: {
         totalCount: 3,
         nodes: [],
@@ -63,6 +66,9 @@ Changed Files: 2 files`,
       author: { login: "test-user" },
       createdAt: "2023-01-01T00:00:00Z",
       state: "OPEN",
+      labels: {
+        nodes: [],
+      },
       comments: {
         nodes: [],
       },