Register OIDC providers through the Icinga Web login button hook

[lippserd]

This PR registers OIDC provider buttons through the login button hook introduced in Icinga Web 2.13. It replaces the legacy login route and view override, as well as the optional loginhooks integration, while preserving provider captions, colors, and logos.

It also:

• Preserves internal return redirects while rejecting external and logout redirects.
• Stores relogin state as a module-local provider route, validates current and legacy cookie values, expires invalid or stale references, and reconstructs redirects from enabled provider names.
• Reports authentication failures without exposing exception details and destroys Jumbojett sessions after both successful and failed authentication.
• Moves backend registration to run.php and removes PHP tag boundaries from configuration.php to prevent premature output.
• Uses Pdo\Mysql::ATTR_INIT_COMMAND and raises the minimum requirements to Icinga Web 2.13, PHP 8.2, and Icinga PHP Library 0.19.

One important note for you to consider:

The repository currently mixes line endings. In this PR, AuthenticationController.php, doc/02-Installation.md, module.info, and run.php use CRLF, while the new LoginButtonHook.php uses LF. Consequently, git diff --check origin/main...HEAD reports 58 added lines as trailing whitespace.

I recommend normalizing line endings in a separate commit or PR so further changes remain easy to review. Add * text=auto eol=lf to .gitattributes, configure the editor to save LF, and run git add --renormalize .. Avoid * -text, because that disables Git's text normalization and preserves the current inconsistency.

[moreamazingnick]

Thank you for your contribution.

It seems a bit off:

in contrast to:

[DeadHunter]

/* public/css/module.less */
&:is(button)[name="btn_submit"] {
  display: flex;
  flex-direction: row;
  align-items: center;
  justify-content: center;
  gap: 1em;
  padding: .5em .75em;
  height: fit-content !important;
  font-weight: bold;
  font-size: 1.25em;
  flex-grow: 1;

  transition: filter ease-in-out 75ms;
  filter: saturate(.5);
  &:hover, &:focus {
    filter: saturate(1);
  }
}

Example with Image:

Example without image:

Example with long caption:

Maybe even larger text if a icon is present:

&:is(button)[name="btn_submit"] {
  /* ... */
  &:has(img) {
    font-size: 1.5em;
  }
  /* ... */
}