Use HTTP Service Metrics and Logging from LogKit

Requires labkit!30 (merged)

Requires labkit!22 (merged)

Requires !157 (merged)

Adds Metrics

This change adds the "standard" promhttp metrics to Pages, implemented by github.com/prometheus/client_golang/prometheus/promhttp as http handler middlewares.

• InstrumentHandlerCounter
• InstrumentHandlerDuration
• InstrumentHandlerInFlight
• InstrumentHandlerRequestSize
• InstrumentHandlerResponseSize
• InstrumentHandlerTimeToWriteHeader

For each of these metrics, we'll have code, method labels.

For example:

# HELP gitlab_pages_http_in_flight_requests A gauge of requests currently being served by the registry.
# TYPE gitlab_pages_http_in_flight_requests gauge
gitlab_pages_http_in_flight_requests 0

# HELP gitlab_pages_http_request_duration_seconds A histogram of latencies for requests to the registry.
# TYPE gitlab_pages_http_request_duration_seconds histogram
gitlab_pages_http_request_duration_seconds_bucket{code="502",method="get",le="0.01"} 5
gitlab_pages_http_request_duration_seconds_sum{code="502",method="get"} 0.009138354999999999
gitlab_pages_http_request_duration_seconds_count{code="502",method="get"} 5

# HELP gitlab_pages_http_request_size_bytes A histogram of sizes of requests to the registry.
# TYPE gitlab_pages_http_request_size_bytes histogram
gitlab_pages_http_request_size_bytes_bucket{code="502",method="get",le="10"} 0
gitlab_pages_http_request_size_bytes_sum{code="502",method="get"} 405
gitlab_pages_http_request_size_bytes_count{code="502",method="get"} 5


# HELP gitlab_pages_http_requests_total A counter for requests to the registry.
# TYPE gitlab_pages_http_requests_total counter
gitlab_pages_http_requests_total{code="502",method="get"} 5

# HELP gitlab_pages_http_time_to_write_header_seconds A histogram of request durations until the response headers are written.
# TYPE gitlab_pages_http_time_to_write_header_seconds histogram
gitlab_pages_http_time_to_write_header_seconds_bucket{code="502",method="get",le="0.01"} 5
gitlab_pages_http_time_to_write_header_seconds_sum{code="502",method="get"} 0.009059493
gitlab_pages_http_time_to_write_header_seconds_count{code="502",method="get"} 5

This change brings parity between the Workhorse metrics, added in gitlab-workhorse!279 (merged) and GitLab Pages.

Adds Logging

This switches Pages over to the LabKit access logger, as used in Workhorse too.

Additionally, it includes several extra fields, including:

1. pages_https HTTPS request?
2. pages_host The hostname
3. pages_project_id The project id

cc @nolith