Kibana version: 7.12

Elasticsearch version: 7.12

Server OS version: N/A

Browser version: Chrome Version 89.0.4389.90 (Official Build) (x86_64)

Browser OS version: Mac OS 11.2.3

Original install method (e.g. download page, yum, from source, etc.): Elastic Cloud

Describe the bug:

Kibana is not recognizing a valid index for defining the boundary used in a tracking containment geo alert. Kibana says no valid indexes found. I have an index pattern created and a properly indexed geo_shape document in the index. I was able to successfully use this index to plot the geo_shape on Kibana Maps.

Steps to reproduce:

1. Define a boundary index:

`
PUT /geo-boundary
{
"mappings": {
"properties": {
"location": {
"type": "geo_shape"
}
}
}
}

GET /geo-boundary/_search

POST /geo-boundary/_doc
{
"location" : {
"type" : "polygon",
"coordinates" : [
[
[
-77.18985,
38.89482
],
[
-77.18985,
38.86802
],
[
-77.10519,
38.86802
],
[
-77.10519,
38.89482
],
[
-77.18985,
38.89482
]
]
]
}
}
`
2. Create a Kibana index pattern for the index.
3. Attempt to create a tracking containment alert.
4. Kibana says it can't find a valid index.

Expected behavior:
Kibana should find and be able to use the index created above.

Screenshots (if relevant):
Kibana Index Pattern:

Tracking Containment Alert Error:

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Any additional context:
cc: @aaronjcaldwell