Added ability to pass in an optional PR number as a parameter (#349)

* Adding pr-number as an optional parameter

* Updated README

* Tests on the pr-number parameter

* Added missing | to table

* re-built script

* Adding support for multiple pr-numbers

* excluded .idea

* Updated readme to reflect that there might be more than one PR

* Additional warning

* Removed unused

* Reformatted and re-built

* Corrected message

* Removed required check

* Added (s) to pull request numbers in the description

Co-authored-by: MaksimZhukov <46996400+MaksimZhukov@users.noreply.github.com>

* Reworded PR-number parameter description

Co-authored-by: MaksimZhukov <46996400+MaksimZhukov@users.noreply.github.com>

* adding getMultilineInput into the tests

* Fixing tests for single pr

* Fixing tests for multiple prs

* Updated README.md to make it more obvious that it can take a list of PRs

* Added example that labels PR's 1-3

* Handled no pull requests better (from code review)

* Handled no pull requests better (from code review)

* Handled missing pull request better (from code review)

* Back out suggested change as it broke the tests

* Rebuilt dist

* Update src/labeler.ts

Co-authored-by: MaksimZhukov <46996400+MaksimZhukov@users.noreply.github.com>

* Added Emphasis to the note

Co-authored-by: MaksimZhukov <46996400+MaksimZhukov@users.noreply.github.com>

* Changed mockInput for pr-number to be string[]

---------

Co-authored-by: MaksimZhukov <46996400+MaksimZhukov@users.noreply.github.com>

__mocks__/@actions/github.ts

@@ -16,7 +16,11 @@ const mockApi = {
       setLabels: jest.fn()
     },
     pulls: {
-      get: jest.fn().mockResolvedValue({}),
+      get: jest.fn().mockResolvedValue({
+        data: {
+          labels: []
+        }
+      }),
       listFiles: {
         endpoint: {
           merge: jest.fn().mockReturnValue({})