[ problem ] github search hits rate limits for some accounts

[LukeLalor]

With the github-search example, abhi was hitting rate limit errors with the github api.

We can work around this in two ways,

1. Limit number of matching on the example. Since we upload json schema, we now are matching hundreds more files than before
2. More efficient file download. We are making far more calls to explore repo structure than needed. Downloading the repo and parsing files locally would be much more efficient.

[LukeLalor]

let's go with 2. This way the fix will also help the github assistant.

clarification: GitHubLoader should be enhanced to download the repository as a whole and check file contents from there rather than downloading on a file by file basis.

As a note, we can use commit hash to determine if we need to check for file diffs at all when updating.