Upgrade alpine base image to 3.15

[knittl]

Closes #2310

[CLAassistant]

All committers have signed the CLA.

[codecov-commenter]

Codecov Report

Merging #2312 (c156bc5) into master (42f2e60) will increase coverage by 2.38%.
The diff coverage is 86.82%.

❗ Current head c156bc5 differs from pull request most recent head 28f598b. Consider uploading reports for the commit 28f598b to get more accurate results

@@            Coverage Diff             @@
##           master    #2312      +/-   ##
==========================================
+ Coverage   72.71%   75.10%   +2.38%     
==========================================
  Files         184      185       +1     
  Lines       14571    14878     +307     
==========================================
+ Hits        10596    11174     +578     
+ Misses       3333     3029     -304     
- Partials      642      675      +33     

Flag	Coverage Δ
ubuntu	75.01% <86.82%> (+2.36%)	⬆️
windows	74.77% <86.82%> (+2.39%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cmd/cloud.go	4.68% <0.00%> (-0.03%)	⬇️
cmd/login_cloud.go	0.00% <0.00%> (ø)
cmd/login_influxdb.go	0.00% <0.00%> (ø)
cmd/ui.go	59.27% <0.00%> (+38.65%)	⬆️
js/modules/modules.go	47.05% <ø> (-35.00%)	⬇️
lib/consts/consts.go	57.14% <ø> (+57.14%)	⬆️
lib/execution.go	92.59% <ø> (ø)
lib/execution_segment.go	92.73% <ø> (ø)
lib/execution_status_gen.go	0.00% <ø> (ø)
lib/fsext/changepathfs.go	92.95% <0.00%> (-1.33%)	⬇️
... and 79 more

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[na--]

Thanks!

[na--]

@knittl, we can merge this as soon as you accept the new CLA. It's basically the same as the old CLA, only adjusted to reflect the acquisition by Grafana and amended so we can use the same CLA text on other repos (e.g. extensions) without contributors having to re-sign a slightly different one for every repo.

[knittl]

@knittl, we can merge this as soon as you accept the new CLA. It's basically the same as the old CLA, only adjusted to reflect the acquisition by Grafana and amended so we can use the same CLA text on other repos (e.g. extensions) without contributors having to re-sign a slightly different one for every repo.

I see. I wondered because I had already signed the CLA in the past. And mentioned that it still said "load impact" instead of "grafana labs". That explains that. Thanks, I have signed the new CLA!