fix: pin github action to exact SHA

* Allow users to run end-to-end tests behind a proxy

* Allow users to run end-to-end tests with a fully-qualified
  and/or private alpine image
* Sort .gitgnore for convenience for future diffs
* Add .idea/ to .gitignore

Allow the user running end-to-end tests to override the
repository's URL in order to use a mirror if need be.

Introduces a new LIST_OF_E2E_TESTS option in order
to select end-to-end tests that will be executed when
calling `make test`.

It uses the tests script's arguments parsing that already
exists.

…reference, and regenerate README.md

* add init-period flag for faster initial sync retries

* address review: alphabetize flags, add readme docs, add e2e tests

* move init flags to alphabetical order in man text

* fix init-timeout e2e test to actually trigger init timeout

* switch init-timeout to init-max-failures per review

- rename flag and helper to count-based (int, not duration)
- skip --max-failures during init when init-max-failures is set so main-max does not override init tolerance
- add SYNC PHASES section to --man and README describing init vs steady-state
- update e2e test to use a bad server path, as suggested in review

* address review: simplify closure, use pflag.Changed for init-max-failures

- move flInitMaxFailures next to flMaxFailures
- default flInitPeriod to flPeriod to kill conditional in hot path
- replace isInitFailuresExceeded + useMainLimit with getMaxFailures closure
- track waitTime as a loop-outer variable, flip on init-done
- detect --init-max-failures via pflag.Changed || GITSYNC_INIT_MAX_FAILURES env; -1 = unlimited, 0 = abort immediately, unset = fall through to --max-failures
- drop now-stale unit tests for removed helpers, update --man and README

…one verification

- Remove redundant `echo "${FUNCNAME[0]}" > "$REPO/file"` in
  filter_partial_clone_blob_none and filter_with_sparse_checkout;
  init_repo already initializes $REPO/file with the funcname.
- Replace the silently-failing `remote.origin.partialclonefilter`
  check (git-sync fetches by URL, not via the "origin" remote, so
  the config keys are never set) with a check for the `.promisor`
  pack marker that `git fetch --filter` produces.

Add "--filter" flag to enable git partial clone

Bumps [golangci/golangci-lint-action](https://github.com/golangci/golangci-lint-action) from 9.2.0 to 9.2.1.
- [Release notes](https://github.com/golangci/golangci-lint-action/releases)
- [Commits](golangci/golangci-lint-action@1e7e51e...82606bf)

---
updated-dependencies:
- dependency-name: golangci/golangci-lint-action
  dependency-version: 9.2.1
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

…angci/golangci-lint-action-9.2.1

build(deps): bump golangci/golangci-lint-action from 9.2.0 to 9.2.1