fix(send): use StringArray flag for url to not split on commas

[piksel]

The send cli command uses StringSlice for the URL argument which will split the input string by ",". This prevents commas from being used in service URLs which is perfectly valid from other usages.
This will change URL to instead use StringArray, which will keep the input intact, but supplying it multiple times adds to the array.
Example:

shoutrrr send -u gotify://localhost/token -u logger:// -m Message -t Title
or
shoutrrr send -u gotify://localhost/token Message -u logger:// -t Title

(first and second non-flag argument are still URL and Message respectively)

[codecov]

Codecov Report

Merging #129 (ccaffc0) into main (84ec2ed) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #129   +/-   ##
=======================================
  Coverage   59.96%   59.96%           
=======================================
  Files          55       55           
  Lines        1184     1184           
=======================================
  Hits          710      710           
  Misses        424      424           
  Partials       50       50           

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