Add script to download fixtures locally

Context

Closes #299914 (closed)

What does this MR do and why?

• Extracts package-related functions into their own files, so that we can reuse them in a script meant to be called outside of the CI.
• Adds a script to download fixtures locally. This will make the live of frontend developers easier.

Does it work?

The refactoring of scripts/gitlab_component_helpers.sh seems to work. I tested it with this test commit: !117672 (0edde93c). The interesting output in the job ishttps://gitlab.com/gitlab-org/gitlab/-/jobs/4115570004#L51: it behaves as expected 🎉.

Test it locally

Before the script

$ pwd
/Users/gitlab/src/gitlab-development-kit/gitlab

$ ls -l tmp/tests/frontend/fixtures-ee
ls: tmp/tests/frontend/fixtures-ee: No such file or directory

Running the script

$ scripts/frontend/download_fixtures.sh --help
Usage: scripts/frontend/download_fixtures.sh [--branch <branch-name>] [--max-commits <number>]

Looks for a frontend fixture package in the package registry for commits on a local branch.

If --branch isn't specified, the script will use the current branch as a commit reference.
If --max-commits isn't specified, the default is 50 commits.

$ scripts/frontend/download_fixtures.sh --max-commits 3
Looking for frontend fixtures for commit dd6174afade056ed372547a36072a1d6e2a6fd0f...
Looking for frontend fixtures for commit 31e6bcd3356fca40ed47a78852e9a2226e318c35...
Looking for frontend fixtures for commit 21cbe69f61762d255ac2bf860d13ef9658ff8e8e...

$ scripts/frontend/download_fixtures.sh --branch master
Looking for frontend fixtures for commit e9a30019d38693efa5102b3c83f0bae172768601...
We have found frontend fixtures at https://gitlab.com/api/v4/projects/278964/packages/generic/fixtures/e9a30019d38693efa5102b3c83f0bae172768601/fixtures-e9a30019d38693efa5102b3c83f0bae172768601.tar.gz!
Downloading from https://gitlab.com/api/v4/projects/278964/packages/generic/fixtures/e9a30019d38693efa5102b3c83f0bae172768601/fixtures-e9a30019d38693efa5102b3c83f0bae172768601.tar.gz ...
Extracting archive to .

After the script

$ ls -l tmp/tests/frontend/fixtures-ee
total 8
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 abuse_reports
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 admin
drwxr-xr-x   5 gitlab  staff  160 Apr 14 14:18 analytics
drwxr-xr-x  13 gitlab  staff  416 Apr 14 14:19 api
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:19 application_settings
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 autocomplete
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 autocomplete_sources
drwxr-xr-x   9 gitlab  staff  288 Apr 14 14:19 blob
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 branches
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 clusters
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 commit
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 deploy_keys
drwxr-xr-x   5 gitlab  staff  160 Apr 14 14:19 ee
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:19 epic
drwxr-xr-x  27 gitlab  staff  864 Apr 14 14:19 graphql
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:19 groups
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 integrations
drwxr-xr-x   5 gitlab  staff  160 Apr 14 14:20 issues
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 jobs
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:20 labels
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 listbox
drwxr-xr-x   5 gitlab  staff  160 Apr 14 14:18 merge_request_diffs
drwxr-xr-x  11 gitlab  staff  352 Apr 14 14:19 merge_requests
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 metrics_dashboard
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 milestones
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:18 pipeline_schedules
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:18 pipelines
drwxr-xr-x   5 gitlab  staff  160 Apr 14 14:19 projects
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:19 projects_json
-rw-r--r--   1 gitlab  staff   27 Apr 14 14:20 returns
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:19 search
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:18 security_configuration
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 sessions
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 settings
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 snippets
drwxr-xr-x  10 gitlab  staff  320 Apr 14 14:18 startup_css
drwxr-xr-x   3 gitlab  staff   96 Apr 14 14:19 tabs
drwxr-xr-x   5 gitlab  staff  160 Apr 14 14:19 timezones
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:20 todos
drwxr-xr-x   4 gitlab  staff  128 Apr 14 14:19 webauthn

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