Add task submodule and PR-triggered integration testing

[luigidematteis]

Description

This PR adds openserverless-task as a git submodule at olaris/ and introduces a workflow that lets maintainers trigger the full acceptance test suite directly from an operator PR.

Task submodule (olaris/)

The operator now carries its own task definitions via a submodule pointing to apache/openserverless-task. When the testing pipeline clones an operator PR branch with --recurse-submodules, it gets the operator code and task definitions in a single checkout.

This enables:

• Testing operator changes against a specific task version in one PR
• Pointing the submodule to a custom task branch when cross-component changes are needed
• No manual branch coordination between repos

Trigger workflow (trigger-testing.yaml)

A new workflow that dispatches operator-pr-test events to openserverless-testing when a maintainer comments /testing <platform> on a PR.

Triggers:

• issue_comment: parses /testing <platform> from PR comments
• workflow_dispatch: manual trigger with pr_number and platform inputs

Guards:

• Only runs for comments from MEMBER, OWNER, or COLLABORATOR (@msciabarra let's understand together if we need a more strict rule)
• Adds a rocket reaction to the comment as acknowledgment

Dispatches a repository_dispatch event to <owner>/openserverless-testing with:

• pr_number, pr_ref, pr_sha — identifies the PR branch
• operator_repo — the fork/repo where the PR lives
• platform — the target test platform (e.g. k3s-amd)

Uses ${{ github.repository_owner }} for the dispatch target, so the same workflow works on forks and upstream.

Secret required

Secret	Purpose
OPENSERVERLESS_TESTING_PAT	GitHub PAT with repo scope on the testing repo, used to fire repository_dispatch events

Companion PR

This PR works together with a PR on openserverless-testing that adds:

• operator-pr-test.yaml workflow (receives the dispatch, builds the image, runs tests)

apache/openserverless-testing#4

How to change the submodule pointer

# Follow main (default)
cd olaris && git checkout main && git pull && cd .. && git add olaris

# Point to a custom task branch
cd olaris && git fetch <remote> <branch> && git checkout FETCH_HEAD && cd .. && git add olaris

[luigidematteis]

The CI passes TAG="$IMG_TAG" to task build-and-load, but all three Taskfiles (TaskfileBuild.yml, TaskfileTest.yml, TaskfileDev.yml) independently compute OPERATOR_TAG via git describe --tags and ignore the passed TAG.
I will close this PR, fix that issue and then I'll reopen it