Replace raw file fetch with api fetch.

[acrogenesis]

Hello!

I'm setting up upptime in a private repository, with a proxy for api.github.com which adds the Authorization header (will release as open-source).

The summary.json being retrieved using raw.githubusercontent.com is a challenge as the pat tokens won't work to retrieve the file.

This PR changes the requests to use ${apiBaseUrl}/repos/${owner}/${repo}/contents/history/summary.json which returns the file for any public repo and if we add the Authorization: Bearer token header for private repos.

[acrogenesis]

What do you think @AnandChowdhary? or would you prefer another approach?

[AnandChowdhary]

The reason I used raw.githubusercontent.com was because they don't have a rate limit as we're only accessing status resources, vs. using the GitHub API, which unauthenticated will have a very small per-minute and per-hour rate limit. Currently the workaround we've been recommending is setting up a proxy (https://upptime.js.org/docs/configuration/#custom-api-base-url), which you can also set for the userContentBaseUrl.

[acrogenesis]

That makes sense, thanks