Manage global options

Both DHCPv4 and DHCPv6 support standard DHCP options [1], [2] defined at global, network, subnet, pool, and host level. This ticket is about implementing the ability to manage (list, add, edit, delete) standard options defined at a global level.

Vendor options and custom options are out of scope and will be handled in separate tickets.

If useful, this work can be split into several tickets (perhaps backend/frontend or doing the list first, then edits, then add/del etc.)

Things to consider:

A list of standard options is well known. Although it keeps growing slowly (both new are defined by IETF and support for them added in Kea).
Older Kea versions support fewer options. Future Kea versions will support more options.
Many options have primitive formats (addresses, lists of integers, lists of addresses, fqdn), but some use record or internal formats. It's ok to initially ignore more complex format, but we will need to support them in the not so distant future. A good example of high visibility option with custom format is DNR.
Kea allows adding option definitions to introduce custom options. This is out of scope for this ticket, but should be done in not so distant future (perhaps in 2025)
There are vendor options that have their own complexity. For the time being, those are out of scope, too.

For vendor options and custom options, it's certainly useful to research the topic now, as the current design should be extensible enough to be able to handle them in the future.