ci: Add pull request template and run commitlint on PR title only

[spetrosi]

We now ensure the conventional commits format only on PR titles and not on commits to let developers keep commit messages targeted for other developers i.e. describe actual changes to code that users should not care about. And PR titles, on the contrary, must be aimed at end users.

For more info, see https://linux-system-roles.github.io/contribute.html#write-a-good-pr-title-and-description

Signed-off-by: Sergei Petrosian spetrosi@redhat.com

[codecov[bot]]

Codecov Report

Patch and project coverage have no change.

Comparison is base (86aa525) 13.86% compared to head (bcd74bf) 13.86%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #363 +/- ## ======================================= Coverage 13.86% 13.86% ======================================= Files 8 8 Lines 1709 1709 Branches 71 71 ======================================= Hits 237 237 Misses 1472 1472 ``` | Flag | Coverage Δ | | |---|---|---| | sanity | `16.54% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=linux-system-roles#carryforward-flags-in-the-pull-request-comment) to find out more.

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