* Add warnings/errors when V2 templates would match same indices… (#54367)
* Add warnings/errors when V2 templates would match same indices as V1
With the introduction of V2 index templates, we want to warn users that templates they put in place
might not take precedence (because v2 templates are going to "win"). This adds this validation at
`PUT` time for both V1 and V2 templates with the following rules:
** When creating or updating a V2 template
- If the v2 template would match indices for an existing v1 template or templates, provide a
warning (through the deprecation logging so it shows up to the client) as well as logging the
warning
The v2 warning looks like:
```
index template [my-v2-template] has index patterns [foo-*] matching patterns from existing older
templates [old-v1-template,match-all-template] with patterns (old-v1-template =>
[foo*],match-all-template => [*]); this template [my-v2-template] will take
precedence during new index creation
```
** When creating a V1 template
- If the v1 template is for index patterns of `"*"` and a v2 template exists, warn that the v2
template may take precedence
- If the v1 template is for index patterns other than all indices, and a v2 template exists that
would match, throw an error preventing creation of the v1 template
** When updating a V1 template (without changing its existing `index_patterns`!)
- If the v1 template is for index patterns that would match an existing v2 template, warn that the
v2 template may take precedence.
The v1 warning looks like:
```
template [my-v1-template] has index patterns [*] matching patterns from existing index templates
[existing-v2-template] with patterns (existing-v2-template => [foo*]); this template [my-v1-template] may be ignored in favor of an index template at index creation time
```
And the v1 error looks like:
```
template [my-v1-template] has index patterns [foo*] matching patterns from existing index templates
[existing-v2-template] with patterns (existing-v2-template => [f*]), use index templates (/_index_template) instead
```
Relates to #53101
* Remove v2 index and component templates when cleaning up tests
* Finish half-finished comment sentence
* Guard template removal and ignore for earlier versions of ES
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
* Also ignore 500 errors when clearing index template v2 templates
Co-authored-by: Elastic Machine <elasticmachine@users.noreply.github.com>
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