make `/rooms` return the url to join each room directly

[Bilb]

Currently a client needs to build the url to join a room from the /rooms response itself.

It would be nice to have that fullUrl (with publicKey) returned as part of the room details directly.

Currently, the returned entries are like this:

[{
"active_users":2170,
"active_users_cutoff":604800,
"admins":["15adbf86be09641d73cad2d25f3fb69084383f230e7f1ae77c51e4451b5b6c1100","15c6807a9933310392a26de0cf9635fba1535b2b9296c9eb6a060481d51b8983a7","15e114772c8577b03f30d2cdbd22d985059ed12b7e47958a8aaf98656b1eedfb08"],
"created":1674795646.097481,
"description":"The official announcement channel for information about Lokinet",
"image_id":27956,
"info_updates":3,
"message_sequence":1675,
"moderators":["15fec070711e4e699ca3ef112104659d4e9f5ab21494e778503d173ed4ec4beb04"],
"name":"Lokinet Updates",
"read":true,
"token":"lokinet-updates",
"upload":false,
"write":false
}
...
]

[jagerman]

SOGS doesn't necessarily have (or know) the base URL you are using, e.g. you might be using https://abc.example.org but that might also be accessible at http://example.org:5678.

[0x330a]

do we set a base url in config that returns the same thing in the sogs -L that we could use?

[majestrate]

if a client is able to request /rooms it should already know that information, without it how could it request that endpoint?

[mdPlusPlus]

This is somewhat related to #185.

[Bilb]

Just found my comment about this issue again in my code, but I wanted this as it is usually how you interact with rest APIs. Each responses gives you the link to use to navigate between pages. Pagination have full for the next and preivous page, etc https://stackoverflow.com/questions/30981727/link-to-another-resource-in-a-rest-api-by-its-id-or-by-its-url I understand that the joining url might not be part of that response though. Just something I kind of expected to get.