ci: add new gha for running frontend e2e tests against specific stack

[yduartep]

create new shared action to run e2e tests against pre-selected stack. You define in which region the selected stack belong, the plugin from where are executed the tests and optionally which other plugins and datasources you want to provision in that stack when starting a Grafana instance. You need to have the playwright configuration and the test specifications in the plugin that run the tests.

Demo:
https://github.com/user-attachments/assets/8fb3f278-a340-4a38-b588-1c685dab941b

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