helm: add arkade chart bump to bump chart versions

[alexellis]

Description

helm: add arkade chart bump to bump chart versions

Motivation and Context

Update patch version of charts automatically, whenever there are adjacent files changed in git for the folder next to Chart.yaml.

Closes #1024

How Has This Been Tested?

With a change to values.yaml in chart/openfaas

$ ~/go/bin/arkade chart bump -w -f ./chart/openfaas/Chart.yaml
$ echo $?
0

$ echo >> ./chart/openfaas/values.yaml
$ ~/go/bin/arkade chart bump -w -f ./chart/openfaas/Chart.yaml
chart/openfaas/Chart.yaml 14.2.16 => 14.2.17
Wrote to: chart/openfaas/Chart.yaml. OK.

diff --git a/chart/openfaas/Chart.yaml b/chart/openfaas/Chart.yaml
index feb526bd..6b5abc43 100644
--- a/chart/openfaas/Chart.yaml
+++ b/chart/openfaas/Chart.yaml
@@ -2,7 +2,7 @@ apiVersion: v2
 type: application
 description: OpenFaaS - Serverless Functions Made Simple
 name: openfaas
-version: 14.2.16
+version: 14.2.17

Thanks to @aryan9600 for his initial work and collaboration on this.