Configurable name transformation for environment variables

[jirkafajfr]

Issue #67

Description of changes:

The action now has additional parameter called name-transformation. Its allowed options are:

• uppercase (default): secret names will be transformed into uppercase. This is how this action historically worked, and is default value.
• lowercase: secret names will be transformed into the lowercase.
• none: no transformation will be performed on the environment variable names and they'll be kept in the same casing as defined in the secret-ids property.

Example 1

- name: Get secrets
  uses: aws-actions/aws-secretsmanager-get-secrets@v2
  with:
    secret-ids: exampleSecretName
    name-transformation: lowercase

will yield environment variable examplesecretname

Example 2

- name: Get secrets
  uses: aws-actions/aws-secretsmanager-get-secrets@v2
  with:
    secret-ids: exampleSecretName
    name-transformation: none

will yield environment variable exampleSecretName

CI changes

I've split integration tests into several branches where each tests different parameter options.

[YuvalShAz]

nit: If we want to cover all the bases with the integ tests it could be useful to add edge cases like blank aliases as well (shouldn't affect the correct-ness of this PR)

Explanation around parseTransformationFunction nullability provided.