Add httptest slow-server timeout test to featureflag client

See merge request !485

Merged-by: Luke Hollinda <lhollinda@gitlab.com>
Approved-by: Luke Hollinda <lhollinda@gitlab.com>
Reviewed-by: GitLab Duo <gitlab-duo@gitlab.com>
Co-authored-by: Elliot Forbes <eforbes@gitlab.com>

chore(deps): update registry.gitlab.com/gitlab-com/gl-infra/common-ci-tasks-images/golang-fips docker tag to v1.26.3

This commit adds the string equivilant of
TestBooleanValueDetails_DefaultTimeoutReturnsDefault, introduced in:
!485

Refactors the slowServerForTimeout function to accept an optional
timeout duration. When no timeout is configured, this timer channel
blocks indefinitely.

This allows us to use the helper function for all tests requiring a
"slow" server.

Merge branch 'renovate/registry.gitlab.com-gitlab-com-gl-infra-common-ci-tasks-images-golang-fips-1.x' into 'master'

chore(deps): update registry.gitlab.com/gitlab-com/gl-infra/common-ci-tasks-images/golang-fips docker tag to v1.26.3

See merge request !490

Merged-by: Bob Van Landuyt <bob@gitlab.com>
Approved-by: Bob Van Landuyt <bob@gitlab.com>
Co-authored-by: GitLab Renovate Bot <ops-contact+gl-common-ci-tasks-self-renovate@gitlab.com>

test(v2/featureflag): test improvements following !485

See merge request !493

Merged-by: Elliot Forbes <eforbes@gitlab.com>
Approved-by: Elliot Forbes <eforbes@gitlab.com>
Co-authored-by: Luke Hollinda <lhollinda@gitlab.com>

chore(deps): update pre-commit hook gitlab-com/gl-infra/common-ci-tasks to v4.2

See merge request !491

Merged-by: Steve Xuereb <sxuereb@gitlab.com>
Approved-by: Steve Xuereb <sxuereb@gitlab.com>
Co-authored-by: GitLab Renovate Bot <ops-contact+gl-common-ci-tasks-self-renovate@gitlab.com>

fix(deps): update module gitlab.com/gitlab-com/gl-infra/platform/runway/fairway to v1.16.0

See merge request !492

Merged-by: Elliot Forbes <eforbes@gitlab.com>
Approved-by: Elliot Forbes <eforbes@gitlab.com>
Co-authored-by: GitLab Renovate Bot <ops-contact+gl-common-ci-tasks-self-renovate@gitlab.com>