[8.x] Do not serialize EsIndex in plan (#119580)

[idegtiarenko]

Backports the following commits to 8.x:

• Do not serialize EsIndex in plan (Do not serialize EsIndex in plan #119580)

[idegtiarenko]

The build is failing with following:

Tests with failures:
 - org.elasticsearch.xpack.esql.ccq.MultiClusterSpecIT.test {date.IN operator with null in list, doesn't find match}
 - org.elasticsearch.xpack.esql.ccq.MultiClusterSpecIT.test {date.IN operator with null in list, doesn't find match, EVAL to check value}

Both tests have associated issues opened:

• [CI] MultiClusterSpecIT test {date.IN operator with null in list, doesn't find match} failing #120348
• [CI] MultiClusterSpecIT test {date.IN operator with null in list, doesn't find match, EVAL to check value} failing #120349

I was able to confirm they are failing without my change when running tests from 8.x

I am going to mute them to unblock this PR.