feat: notify user their version of dbc is out of date

[zeroshade]

closes #259

[ianmcook]

@zeroshade what sets the x-dbc-latest header when a new dbc version is released?

[ianmcook]

I think this should probably just fail silently if it can't fetch the latest available dbc version. Telling the user that it didn't succeed is not really helpful or actionable.

[ianmcook]

@amoeba any clever ideas about how to make this less annoying for users who are making the conscious choice not to upgrade (at least not right now)?

[zeroshade]

@zeroshade what sets the x-dbc-latest header when a new dbc version is released?

Cloudfront function on the distribution for downloading dbc (we use it for the install scripts). It maps latest -> the latest version. So I added a check for the case where the request is just / as the path

[zeroshade]

I think this should probably just fail silently if it can't fetch the latest available dbc version. Telling the user that it didn't succeed is not really helpful or actionable.

That's currently the case. It fails silently if it fails. Notice in main.go we ignore the error returned if it's not nil and just move on

[eitsupi]

I haven't looked into how existing software implements such functionality, but I wonder if there are cases where distribution channels might want to disable such functionality?
I imagine there might be a need to be able to disable this functionality at build time.

[zeroshade]

We could create a build flag and allow controlling whether it does this check with a build tag if everyone thinks that would be a good idea. @ianmcook @amoeba @esadek what do you think?