Fix notifications listener leak in threat intel monitor

[eirsep]

Description

1. Fixes listener leak in notification success
2. marks execution succeeded if findings generated and alerts creation fails.
3. marks execution succeeded if findings and alerts are generated but send notfication fails.

we are doing 2. and 3. to avoid findings from being generated repeatedly and moving the marker forward for last seen docs in monitor metadata.

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[opensearch-trigger-bot]

The backport to 2.16 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/security-analytics/backport-2.16 2.16
# Navigate to the new working tree
pushd ../.worktrees/security-analytics/backport-2.16
# Create a new branch
git switch --create backport-1356-to-2.16
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 98edd700183b169a439d246142dd7044fa57edb1
# Push it to GitHub
git push --set-upstream origin backport-1356-to-2.16
# Go back to the original working tree
popd
# Delete the working tree
git worktree remove ../.worktrees/security-analytics/backport-2.16

Then, create a pull request where the base branch is 2.16 and the compare/head branch is backport-1356-to-2.16.