use a comma separated list of IPs for purge_allow_ip

[jpappa200]

Closes: #7232
If a profile has multiple parameters with the same name and config file, the layered profile approach will only use one parameter. this has become an issue with ip_allow.yaml because we add multiple single IPs to allow purge from all Traffic Ops servers.
I have updated ipallowdotyaml.go to handle a comma separated list of IP addresses in a single parameter.

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Which Traffic Control components are affected by this PR?

• Traffic Control Cache Config (t3c, formerly ORT)

What is the best way to verify this PR?

create a parameter Name: purge_allow_ip Config File: ip_allow.config Value: comma separated list of IPs. associate new parameter with a profile and remove all other purge_allow_ip parameters. Queue updates and run t3c. when finished you should see all IPs allowing purge and if you queue and run again ip_allow.yaml doesn't change.

If this is a bugfix, which Traffic Control versions contained the bug?

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

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@@            Coverage Diff            @@
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  Partials          ?     1526           

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golib_unit	53.09% <0.00%> (?)
grove_unit	4.60% <0.00%> (?)
t3c_generate_unit	24.96% <0.00%> (?)
traffic_monitor_unit	20.43% <0.00%> (?)
traffic_ops_unit	19.81% <0.00%> (?)
traffic_stats_unit	10.41% <0.00%> (?)

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[ocket8888]

FWIW, separating by lines may be easier to read, and is pretty unix-like-standard. Just one man's opinion.

[traeak]

Looks okay. Document does mention to use a parameter with comma separated ips to specify multiple addresses.