updatecli: dynamic specs

[v1v]

What does this PR do?

• Use values.yml to define the configuration to be used when running the updatecli apply, see https://www.updatecli.io/docs/commands/updatecli_apply/#updatecli-apply
• Use updatecli scm to fetch the specs in elastic/apm and elastic/apm-data under the different folders.
• To update those files, use tar with the shell target.

Test

I iterated in the existing GitHub action by using the upstream branch:

• https://github.com/elastic/apm-agent-go/actions/runs/7652269076 ran successfully.

Locally:

GITHUB_WORKSPACE=/tmp \
  PATH=/opt/homebrew/bin:$PATH \
  GIT_USER="Victor Martinez" \
  GIT_EMAIL="VictorMartinezRubio@gmail.com" \
  GITHUB_TOKEN=$(gh auth token) \
  updatecli apply --config .ci/updatecli/updatecli.d --values .ci/updatecli/values.yml --debug

or without pushing any changes

GITHUB_WORKSPACE=/tmp \
  PATH=/opt/homebrew/bin:$PATH \
  GIT_USER="Victor Martinez" \
  GIT_EMAIL="VictorMartinezRubio@gmail.com" \
  GITHUB_TOKEN=$(gh auth token) \
  updatecli apply --config .ci/updatecli/updatecli.d --values .ci/updatecli/values.yml --push=false --debug

additionally, you can change the org from elastic to your own GitHub avatar.