Allow lowercase transformers key

[olblak]

Fix #655
Fix #653

• Convert transformer to a struct which allows to generate jsonschema fields
• Deprecate non lowercase transformer fields such as semverInc becomes semverinc

Test

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

cp pkg/core/transformer
go test
 go build -o bin/updatecli && ./bin/updatecli jsonschema --directory schema

Ensure that jsonschema contains transformers field

Additional Information

Tradeoff

A side effect of converting transformer to a stuct means that the two following examples are accepted and means different things

*Order is guaranteed because of the list

# v1.0.0-alpha
transformers:
    - trimsuffix: alpha
    - replace:
          from: alpha
          to: beta

Order is not guaranteed because of the map

# v1.0.0-alpha
transformers:
    - trimsuffix: alpha
      replace:
          from: alpha
          to: beta

Potential improvement

[olblak]

Considering that this pullrequest is fully backward compatible, I am going to merge it and proceed.
The three main advantages of this pulllrequest

1. Allow to use lowercase transform key so addprefix instead of addPrefix which is more consistent with the naming convention used now
2. Generate jsonschema for transformer which is more convenient when writing Updatecli manifest from IDE support jsonschema store

[olblak]

for context, I move the updatecli manifest in the e2e directory under e2e/updatecli.d so Vscode could enable jsonschema validation

[olblak]

After adding e2e tests for transformers where I test both the old and new syntax. I consider this ready to be merged