secrets/awskms: update the example for the AWS ARN use case

[h27771420]

As the title.

AWS ARN can't be parsed by url.Parse() directly, because there are couple : in it. (e.g., "awskms://arn:aws:kms:us-east-1:932528106278:key/8be0dcc5-da0a-4164-a99f-649015e344b5?region=us-east-1")
Then I fell into that trap💀, so here is a PR to avoid further victims.

The issue has been solved, but the use case isn't updated.

1. issue: secrets/awskms: AWS KMS keys cannot be specified by ARN #2808
2. fix: secrets/awskms: support ARNs in URLs by allowing empty Host #2811

[vangent]

Please run

internal/website/gatherexamples/run.sh > internal/website/data/examples.json

and add the commit.

[codecov]

Codecov Report

Merging #3320 (2c67939) into master (486d484) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3320      +/-   ##
==========================================
+ Coverage   77.45%   77.48%   +0.02%     
==========================================
  Files         104      104              
  Lines       13933    13933              
==========================================
+ Hits        10792    10796       +4     
+ Misses       2380     2377       -3     
+ Partials      761      760       -1     

see 2 files with indirect coverage changes

[vangent]

Thanks for the fix!