Template priority to be int or max value a long

[gemaliano]

Elasticsearch version (bin/elasticsearch --version): 7.16.2

Steps to reproduce:

When running GET _cat/templates?v we see some templates with priority 2147483647

.watch-history-13                         [.watcher-history-13*]       2147483647        13      []
.ml-state                                 [.ml-state*]                 2147483647        7160299 []
ilm-history                               [ilm-history-5*]             2147483647        5       []
.slm-history                              [.slm-history-5*]            2147483647        5       []
.ml-anomalies-                            [.ml-anomalies-*]            2147483647        7160299 []
.ml-notifications-000002                  [.ml-notifications-000002]   2147483647        7160299 []
.ml-stats                                 [.ml-stats-*]                2147483647        7160299 []

Priority is a long value so we are able to override the template using higher value than 2147483647 (which is the max int value).
We are not supposed to override these templates, so ideally we should have priority an int or priority value to be max long.

[elasticmachine]

Pinging @elastic/es-data-management (Team:Data Management)

[dakrone]

I believe this was historically because legacy templates used an int for the order (which roughly maps onto the composable index template's priority), so it used to be the maximum it can be.