Rate limiter instrumentation

Closes #154 (closed).

# HELP limiter_block_duration_milliseconds Duration the rate limiter blocked for deciding to allow/block the call
# TYPE limiter_block_duration_milliseconds histogram
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="0"} 0
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="5"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="10"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="25"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="50"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="75"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="100"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="250"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="500"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="750"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="1000"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="2500"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="5000"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="7500"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="10000"} 1
limiter_block_duration_milliseconds_bucket{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",le="+Inf"} 1
limiter_block_duration_milliseconds_sum{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version=""} 0.014292
limiter_block_duration_milliseconds_count{allowed="true",limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version=""} 1
# HELP limiter_limit Limit for the rate limiter
# TYPE limiter_limit gauge
limiter_limit{limiter_name="agent_connection",otel_scope_name="kas",otel_scope_version="",unit="{connection/token/m}"} 40000
limiter_limit{limiter_name="gitaly_client_global",otel_scope_name="kas",otel_scope_version="",unit="{refill/s}"} 30
limiter_limit{limiter_name="gitlab_client",otel_scope_name="kas",otel_scope_version="",unit="{refill/s}"} 50