fix(multilocation_alert_condition): make violation_time_limit_seconds nearly consistent with its usage in nrql_alert_condition

[pranav-new-relic]

As reported in #2475, the current validation against the argument violation_time_limit_seconds does not allow using the value 259200 (30 days), while this is supposed to be allowed as per New Relic's docs.

This attribute violation_time_limit_seconds is also used in newrelic_nrql_alert_condition to serve the same usecase, but it appears that the validation and other schema specifications are not the same in both of these resources. This PR aims at correcting the above.

Additionally, since 0 has been permitted to be valid value of the violation_time_limit_seconds argument so far (though values of violation_time_limit_seconds are expected to ∈ [300, 2592000] like specified with newrelic_nrql_alert_condition), a DiffSuppressFunc has been added to violation_time_limit_seconds in the multilocation_alert_condition resource to handle the case in which users specify 0, but the API defaults 0 to 259200 (3 days), and hence, differences need to be suppressed.

[codecov-commenter]

Codecov Report

Merging #2493 (febc019) into main (cbed7ad) will decrease coverage by 0.03%.
The diff coverage is 36.36%.

@@            Coverage Diff             @@
##             main    #2493      +/-   ##
==========================================
- Coverage   33.90%   33.87%   -0.03%     
==========================================
  Files          91       91              
  Lines       24900    24900              
==========================================
- Hits         8442     8435       -7     
- Misses      16303    16309       +6     
- Partials      155      156       +1     

Files	Coverage Δ
newrelic/resource_helpers.go	1.38% <ø> (ø)
newrelic/resource_newrelic_nrql_alert_condition.go	30.66% <ø> (ø)
...wrelic_synthetics_multilocation_alert_condition.go	43.82% <36.36%> (-4.33%)	⬇️

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[pranav-new-relic]

This is supposed to be 300 - 2592000 as also specified in New Relic docs, but I've added 0 as the minimum as this resource is already in use with 0 as a valid value of violation_time_limit_seconds.

However, the current behaviour of the API is such that if 0 is given as a value against this argument, the API defaults it to 259200 seconds. This is why the below DiffSuppressFunc has been added.