Fix sending LSP4IJ integration build results to Slack channel

[vaisakhkannan]

Fixes #759

I have added code for sending LSP4IJ integration build results to Slack channel. Currently I am using the same channel lsp4ij-monitoring and using the same secret variable SLACK_WEBHOOK_URL

I have tested with the changes in the PR #864 which is opened against the issue #815

[vaisakhkannan]

Output screenshot :

We will receive a single Slack notification with the overall build status. If any of the builds fail, the status will be reported as "failed". If all builds succeed, the status will be reported as "succeeded".

Link for the reference : https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10055468368
https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10053225899

[vaisakhkannan]

Link for the reference latest Cron Job build

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10072710102

Example builds in different cases:

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10092590989 --> Status -- Failed ( 2nd Matrix tag is failing )

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10092549050 --> Status -- Succeeded in all builds

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10092565454 --> Status -- Failed ( 3rd Matrix tag is failing )

[anusreelakshmi934]

Looks good

[vaisakhkannan]

I marked this PR as draft because I need to test with multiple open PRs of LSP4IJ Repo

[vaisakhkannan]

Today, I tried to test the changes in this PR with multiple open PRs of LSP4IJ. Since it only has one PR without merge conflicts, I used my fork repo API to test with multiple open PRs. I found an issue where the Cron Job builds are taking PRs with merge conflicts.

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10091019128

PR number 31 is the only PR which do not having merge conflicts. But Cron Job builds taking all the PRs.

Upon further inspection of the API, I discovered that there are several other values present for mergeable_state.

We are currently checking only one condition ( if [[ "$mergeable_state" != "dirty" ]] ). Therefore, I believe we need to add an additional condition check to confirm PRs without merge conflicts.

[vaisakhkannan]

Reference Link of GHA results:
https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10194863913
https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10175374062
https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10191777126/attempts/1

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10194515131 --> One job Success & one job failure

https://github.com/vaisakhkannan/liberty-tools-intellij/actions/runs/10192703426 --> One os matrix failure example

[mrglavas]

Reviewed with Vaisakh and the team this morning. I just reviewed the computed build status for the reference builds. It all looked good, so I'm approving this PR now. Great work! Thanks again.