fix: HelmChart always bumps Chart Version

[olblak]

Fix #693

\When used with a scm, the helmchart resource now monitors the Chart.yaml from the branch mentioned by the scm resource. It tries to be smart by either using the computed version from the base branch, or it uses without modification the one mentioned in the new temporary branch if the later one is newer.

Test Scenario

Pipeline 1:
*  `1.0.0` (from base branch) -> apply patch update -> `1.0.1`
* no temporary branch yet so creating a new one with version to `1.0.1`

Pipeline 2: 
*  `1.0.0` (from base branch) -> apply patch update -> `1.0.1`
* tmp branch already set to ``1.0.1` so nothing else to do

Pipeline 3: 
*  `1.0.0` (from base branch) -> apply minor update -> `1.1.0`
* tmp branch set to ``1.0.1` which is older than `1.1.0` 
* Updating temporary branch to `1.1.0`

Pipeline 4: 
*  `1.0.0` (from base branch) -> apply patch update -> `1.0.1`
* tmp branch set to ``1.1.0` which is newer than `1.0.1` nothing else to do 

Test

To test this pull request, you can run the following commands:

cd <to_package_directory>
go test

Additional Information

Tradeoff

Potential improvement

• While working on this pullrequest, I realise the plugin would only update Chart.yaml and don't try to handle Chart.yml which I think is an accepted file extension.