Mostly merge from master plus a few more that were still in the
stable/15.7 code base.

(cherry picked from commit 343aa7df)
(cherry picked from commit 692a8f77)
(cherry picked from commit f8b281e9)
(cherry picked from commit 8d2e334b)
(cherry picked from commit b9346703)
(cherry picked from commit 418b13af)
(cherry picked from commit b235235d)
(cherry picked from commit e259289f)
(cherry picked from commit 68fed4c9)
(cherry picked from commit 8757d000)
(cherry picked from commit 33394bdc)
(cherry picked from commit 8cccf2e8)
(cherry picked from commit eb29c782)
(cherry picked from commit 3fcda571)
(cherry picked from commit 4ff0b327)

(cherry picked from commit b980171c)

https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_server.php#L1175
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_server.php#L1178 bis 1182
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export_shared.php#L175
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export_shared.php#L191
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export_shared.php#L206
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export_shared.php#L210
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export_shared.php#L214
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L340
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L369
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L373
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L387
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L402
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L406
https://github.com/opnsense/core/blob/master/src/www/vpn_openvpn_export.php#L410
(cherry picked from commit 094ad4e8)

(cherry picked from commit 7b7e6150)

(cherry picked from commit f9451641)

(cherry picked from commit 608dbd9a)

(cherry picked from commit 71f7dbc3)

(cherry picked from commit 235169e2)

(cherry picked from commit 5cf5ef0c)

(cherry picked from commit d3827091)

(cherry picked from commit 5e5ac2a0)

(cherry picked from commit 605fb08c)

(cherry picked from commit 6514a161)

(cherry picked from commit 0dea657b)

(cherry picked from commit 98678fb1)
(cherry picked from commit b06e42ae)
(cherry picked from commit 26708b04)

(captiveportal, new) change rc script to use cp instead of rsync (which is not installed by default) and change file ownership to chroot user

(cherry picked from commit 9bbca9c2)

(cherry picked from commit 14c59c64)
(cherry picked from commit d37aff72)

(cherry picked from commit efb83c62)

(cherry picked from commit debaee82)

(cherry picked from commit 10a0fd8e)

(cherry picked from commit 06a7ea48)

(cherry picked from commit 762952c3)

(cherry picked from commit 3e0e936b)

Revert "(legacy) remove caching of filter interfaces, likely suspect of https://github.com/opnsense/core/issues/451"

This reverts commit 2f863fa9.

This reverts commit 8ee0c0a2.

Revert "(legacy) kill "interface cache", let's not try to cache things that may change during the session... all for saving a ifconfig call."

This reverts commit 4c48ab5d.

This reverts commit bc6bbc40.

This reverts commit 47aaef9d.

This reverts commit 5474af27.

This reverts commit d4f27bc4.

This reverts commit 7b1f2d92.

PR: https://forum.opnsense.org/index.php?topic=1730.0
(cherry picked from commit fb352932)

(cherry picked from commit 877ad265)

I know, gettext('2') et al looks stupid, but not having a complete
gettext() wrapping only leads to bugs later on...

(cherry picked from commit 358cfb02)

(cherry picked from commit c00c5b3f)

(cherry picked from commit ec86345d)

(cherry picked from commit 4760cfda)

(cherry picked from commit 83554e53)

(cherry picked from commit d8946545)