[feat]: Create `<pf-alert>` element

[zeroedin]

Create <pf-alert> element.

Reference: Alert

Notes to developer:

Prior Art found in <rh-alert>. This component could be backported to use Patternfly tokens.

Features such as the expandable and truncated alerts could be excluded in the initial implementation and wouldn't be considered blocking.

[bennypowers]

Closed by #2951