Add --ignore-path to flux create source

[stefanprodan]

We need to add a new arg (string array) to flux create source git and flux create source bucket that populates the ignore spec filed, each arg would add a new line to the ignore value e.g.:

flux create source git podinfo \
--url=https://github.com/stefanprodan/podinfo \
--branch=master \
--ignore-path=".git/" \
--ignore-path=".github/" \
--export

The above command will generate:

apiVersion: source.toolkit.fluxcd.io/v1beta2
kind: GitRepository
metadata:
  name: podinfo
  namespace: flux-system
spec:
  interval: 5m
  url: https://github.com/stefanprodan/podinfo
  ref:
    branch: master
  ignore: |
    .git/
    .github/

[takirala]

Addressed in #2767