docs: add more api specs

[IronCore864]

Adding more endpoints to the OpenAPI spec.

Refactor

• Refactor existing endpoint parameter examples and remove them.
• Refactor existing request body examples, but keep only one.
• Refactor non-directly used component names as lowercase.
• Reorder API groups according to pebble help output.

Style updates

• Similar to hiding the input box for parameters, hide the select drop-down (because one newly added endpoint has an enum).

Newly added specs

• /v1/system-info. The code is here, and the possible boot-id value is here.
• /v1/health. The code is here.
• /v1/changes, code is here.
• /v1/changes/{id}, both GET and Post. Code: get, post.
• /v1/services/{name}, not implemented in the code
• /v1/checks, code.

Sorry for this big PR, but it's only logical::

• /v1/system-info is more of a miscellaneous endpoint that doesn't belong to any group/tag.
• Since /v1/health is another public API besides /v1/system-info, I included it as well, only to find out later that /v1/changes belongs to the same group so I included it in the same PR.
• Since we already have some services and changes spec, to make the services and changes group/tag complete, I included other endpoints of the same group.

[dwilding]

Thanks! Approving so that you can merge later. I've added specific questions/suggestions (see the comments) and I have a couple more thoughts:

• For the two unsupported endpoints, I think it's best to exclude them from the doc if possible. To make it easier to navigate around the other endpoints

• I'm a bit confused about GET /v1/health - Does this return a 200 response for healthy: true and healthy: false? From reading the code, it seems like the response for healthy: false is http.StatusBadGateway (code 502). Maybe I misunderstood, but don't we need two different responses for this endpoint?

[IronCore864]

Thanks! Approving so that you can merge later. I've added specific questions/suggestions (see the comments) and I have a couple more thoughts:

• For the two unsupported endpoints, I think it's best to exclude them from the doc if possible. To make it easier to navigate around the other endpoints

Removed.

• I'm a bit confused about GET /v1/health - Does this return a 200 response for healthy: true and healthy: false? From reading the code, it seems like the response for healthy: false is http.StatusBadGateway (code 502). Maybe I misunderstood, but don't we need two different responses for this endpoint?

Yes, it's 200 when healthy is true and 502 when false. However, in a discussion with Ben earlier, we agreed to only show responses for 200 and not 4xx/5xx responses, which are shown at the beginning of the doc, so I have only one response/example here.