[FIX] website: position step connectors relative to columns

Since [1] when Bootstrap 5 was introduced, the position of the
connectors between steps of the "Steps" block is wrongly computed.

The left offset of the connectors between steps is computed as 50% of
the column width + half the size of the content it connects to.
In Bootstrap 4 the columns are positioned as relative.
In Bootstrap 5 the columns are positioned as static.
Because of this "50% of the column width" became "50% of the row width"
in Bootstrap 5.

This commit makes the specific columns of this snippet positioned as
relative so that the offset calculation get back to its former result.

Steps to reproduce:
- Drop a "Steps" block.
=> Connectors are wrongly positioned, even spanning outside the page.

[1]: https://github.com/odoo/odoo/commit/971e5a91aab96d36129a823e03f1f9f1b1293968

task-2729177

closes odoo/odoo#96071

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/website/static/src/snippets/s_process_steps/000.scss

@@ -15,6 +15,7 @@
     @include media-breakpoint-up(lg) {
         overflow-x: hidden;
         .s_process_step {
+            position: relative;
             .s_process_step_icon {
                 position: relative;
                 z-index: 1;

addons/website/static/src/snippets/s_process_steps/001.scss

@@ -2,6 +2,8 @@
     $process-step-icon-size: 5rem;
 
     .s_process_step {
+        position: relative;
+
         .s_process_step_icon {
             position: relative;
             margin: $grid-gutter-width 0;