Rename metrics with a browser prefix

[ankur22]

Description of changes

k6 emits http metrics and other metrics (builtin metrics) which are useful for the user to work out how their API under test is behaving. The browser module currently works with these same metrics.

While working on an issue to identify why failed metrics requests weren't being accounted for, it became apparent that there was a mismatch in the tags that were being attached to the metrics between k6 and browser. This could affect the output summary and results in user's dashboards.

This also brought to light that these metrics heavily depend on the http implementation, and so the http metrics that the browser module emits will skew the results of the http metrics that k6 emits.

The first step in mitigating such issues is to easily distinguish between the two metrics. Custom metrics (which are clones of the builtin http metrics from k6) have been added and prefixed with browser_. This also follows the best practices of prometheus metric naming.

Closes: #883

Difference in Summary Results

+ browser_data_received..............: 27 kB  28 kB/s
+ browser_data_sent..................: 1.1 kB 1.1 kB/s
+ browser_http_req_connecting........: avg=79.66ms  min=0s       med=0s       max=239ms    p(90)=191.2ms  p(95)=215.09ms
+ browser_http_req_duration..........: avg=237.38ms min=112.65ms med=223.28ms max=376.22ms p(90)=345.63ms p(95)=360.92ms
+ browser_http_req_receiving.........: avg=111.33ms min=110ms    med=110ms    max=114ms    p(90)=113.2ms  p(95)=113.6ms 
+ browser_http_req_sending...........: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
+ browser_http_req_tls_handshaking...: avg=43.33ms  min=0s       med=0s       max=130ms    p(90)=104ms    p(95)=116.99ms
+ browser_http_reqs..................: 3      3.159238/s
browser_web_vital_fcp.........: avg=504.09ms min=504.09ms med=504.09ms max=504.09ms p(90)=504.09ms p(95)=504.09ms
browser_web_vital_fcp_good....: 1      1.109633/s
browser_web_vital_ttfb........: avg=347.09ms min=347.09ms med=347.09ms max=347.09ms p(90)=347.09ms p(95)=347.09ms
browser_web_vital_ttfb_good...: 1      1.109633/s
+ data_received......................: 0 B    0 B/s
+ data_sent..........................: 0 B    0 B/s
- data_received.................: 27 kB  30 kB/s
- data_sent.....................: 1.1 kB 1.2 kB/s
- http_req_connecting...........: avg=70.33ms  min=0s       med=0s       max=211ms    p(90)=168.8ms  p(95)=189.89ms
- http_req_duration.............: avg=208.79ms min=92.41ms  med=185.53ms max=348.44ms p(90)=315.86ms p(95)=332.15ms
- http_req_receiving............: avg=93.66ms  min=89ms     med=92ms     max=100ms    p(90)=98.4ms   p(95)=99.2ms  
- http_req_sending..............: avg=0s       min=0s       med=0s       max=0s       p(90)=0s       p(95)=0s      
- http_req_tls_handshaking......: avg=41ms     min=0s       med=0s       max=123ms    p(90)=98.4ms   p(95)=110.69ms
- http_reqs.....................: 3      3.328899/s
iteration_duration............: avg=901.83ms min=901.83ms med=901.83ms max=901.83ms p(90)=901.83ms p(95)=901.83ms
iterations....................: 1      1.109633/s

NOTE: data_received and data_sent are still be printed, even though the browser module is no longer interacting with these metrics. This is a known issue and will be looked into with k6.

Testing

You should be able to run any of the example tests.

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[ka3de]

I think this makes more sense!
LGTM.

[inancgumus]

Nice 👏