Replace dots in branch names by dash in Terraform labels

[mrodm]

This PR adds the dot character as a new one to be replaced by a dash in the labels used by terraform.

Error when trying to use dots:

Error: Error creating instance: googleapi: Error 400: Invalid value for field 'resource.labels': ''. Label value 'elastic-dependabot-go-modules-helm.sh-helm-v3-3.14.1' violates format constraints. The value can only contain lowercase letters, numeric characters, underscores and dashes. The value can be at most 63 characters long. International characters are allowed., invalid

Example including dot in the tr command:

 $ BUILDKITE_BRANCH="elastic:dependabot/go_modules/helm.sh/helm/v3-3.14.1"
 $ echo "$BUILDKITE_BRANCH" | tr '[:upper:]' '[:lower:]' | tr '_/\:. ' '-'
elastic-dependabot-go-modules-helm-sh-helm-v3-3-14-1

Relates #1683

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: d7e27d2

cc @mrodm