optimize sequence number calculation and reduce search requests in doc level monitor execution

[eirsep]

Optimize sequence number calculation and reduce search requests by n, where n is number of shards being queried in the execution

Issue #, if available:

1409

Description of changes: Use the first shard search request on each shard to compute max sequence number instead of making a search call simply to calculate the value. Fetch data in descending order of sequence numbers to directly calculate the max seq_no

New heuristic: take an example of one shard in current iteration: previous seq_no = 10000, current max seq_no= 40000

first iteration of search shard(which also determines the max sequence number) : TO=int_max, FROM=prev_seq_no : calculate max_seq number second iteration : TO=max_seq_no-10000 FROM=prev_seq_no further iterations : TO=TO-10000 FROM=prev_seq_no till while to>from

in first iteration we get first 10k results and also calculate the max sequence number in second iteration we reduce (TO) variable to maxSeqNo -10000 and query again and we continue this loop until we have seen all docs up untill the previous sequence number

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[opensearch-trigger-bot[bot]]

The backport to 2.x failed:

The process '/usr/bin/git' failed with exit code 128

To backport manually, run these commands in your terminal:

# Navigate to the root of your repository
cd $(git rev-parse --show-toplevel)
# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add ../.worktrees/alerting/backport-2.x 2.x
# Navigate to the new working tree
pushd ../.worktrees/alerting/backport-2.x
# Create a new branch
git switch --create backport-1445-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 faaf5520a71ce1b213968eadace6e7689320d997
# Push it to GitHub
git push --set-upstream origin backport-1445-to-2.x
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/alerting/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport-1445-to-2.x.