chore(deps): update registry.gitlab.com/gitlab-com/gl-infra/common-ci-tasks-images/golang-fips docker tag to v1.26.2

Restructures the Health endpoints section into Liveness, Readiness,
and a new Writing safe readiness checks block.

The new section explains the readiness semantic (can-I-serve-traffic,
not are-my-deps-healthy), what to include and exclude, the cascading
failure pattern, and Kubernetes probe configuration guidance.

Adds a ### Startup section explaining when to use a startup probe,
why /-/readiness is the right endpoint to reuse, how to size
failureThreshold for worst-case startup time, and when a custom
startup endpoint makes sense.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Health endpoints (/-/liveness, /-/readiness) and /-/metrics are now
served exclusively on Config.ProbeAddr (default :9090). The main port
serves application traffic only.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Go 1.22+ loop variables are scoped per iteration; the name := name copy
is unnecessary and flagged by golangci-lint.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Tests that call Start without ProbeAddr defaulted to :9090, causing
port conflicts when tests ran concurrently.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Reflow long single-line paragraphs to one sentence per line, apply
M_Alvarez's wording suggestions for the startup probe section, improve
active voice on the readiness what-to-check bullet, align YAML comment
spacing, and remove the unrelated docs/ gitignore entry.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

TestLiveness_IncludesBuildInfo, TestLiveness_OmitsBuildInfoWhenEmpty,
and TestReadiness_IncludesBuildInfo were written against srv.ServeHTTP
which no longer routes /-/liveness or /-/readiness now that those
endpoints moved to the dedicated probe server. Rewrite them to use
startProbeServer and hit the probe address via HTTP, consistent with
every other health endpoint test in the file.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Co-authored-by: Matias Alvarez <malvarez@gitlab.com>

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 v1.26.2

See merge request !451

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>

docs(v2/httpserver): add readiness check best practices

Closes gitlab-org/quality/quality-engineering/team-tasks#4381

See merge request !402

Merged-by: Elliot Forbes <eforbes@gitlab.com>
Approved-by: Matias Alvarez <malvarez@gitlab.com>
Reviewed-by: GitLab Duo <gitlab-duo@gitlab.com>
Reviewed-by: Matias Alvarez <malvarez@gitlab.com>