[8.10] Restore version skipping for position fields and synthetic source (elastic#100827)

* [TEST] Mute all tsdb tests in mixedClusterTests, for versions 8.7 - 8.10 (elastic#100805)

* Don't print synthetic source in mapping for bwc tests

* Move comment.

* Don't print synthetic source in mapping for bwc tests #2

* Don't print synthetic source in mapping for bwc tests #2

* Revert "Don't print synthetic source in mapping for bwc tests #2"

This reverts commit 034262c.

* Revert "Don't print synthetic source in mapping for bwc tests #2"

This reverts commit 44e8156.

* Revert "Don't print synthetic source in mapping for bwc tests (elastic#100572)"

This reverts commit 9322ab9.

* Exclude synthetic source test from mixedClusterTests

* Update comment.

* Mute all tsdb tests in mixedClusterTests

This is an interim step to stop sporadic test failures, while we try to
fix version skip for mixed cluster tests.

* Remove old exclusion

* Add aggregations too

* Mute tests for versions between 8.7-8.10

* Remove mute

* Fix skip for position fields

* Restore version skip for synthetic source

Author: kkrik-es

rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/tsdb/20_mapping.yml

@@ -424,6 +424,9 @@ nested fields:
 
 ---
 "Synthetic source":
+  - skip:
+      version: " - 8.9.99"
+      reason: "Synthetic source shows up in the mapping in 8.10"
   - do:
       indices.create:
         index: tsdb-synthetic