[Fleet] Don't add ecs@mappings component template when dynamic: runtime is used.

[jsoriano]

Describe the feature:

Don't add ecs@mappings component template to index templates managed by Fleet that use dynamic: runtime.

Describe a specific use case for the feature:

When using dynamic: runtime at the data stream level, the package developer probably don't want to provide mappings for fields that are not explicitly defined in the package. We have seen cases where the inclusion of ecs@mappings starts applying mappings to fields that were not previously mapped. This can cause issues with intermediary objects.

More specifically, we saw that the APM package was using dynamic: runtime and was not providing mappings for related.ip and related.host. After 8.13 this package started using ecs@mappings. Then mappings were added for these fields, but not for the intermediary object related, what causes issues.

Related issues:

• In [Fleet] Create intermediate objects when using dynamic mappings #169981 we solved an issue with intermediary objects for mappings generated by fleet.
• ecs@mappings is added to all data streams since Add reference to ecs@mappings for each index template #174855.

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)