Improved tera errors

[UebelAndre]

This fixes some annoyingly vague errors:

Error: Raze failed to render with cause: "Failed to render 'templates/remote_crates.bzl.template'

becomes

Error: Raze failed to render with cause: "Failed to render 'templates/remote_crates.bzl.template'
└─Template 'templates/partials/remote_crates_patch.template' not found"

[UebelAndre]

@damienmg Hey, can I get your eyes on this? It's small (and I promise not to add anything to it 😅)

[damienmg]

What is the relation between the 3 commits? Shouldn't that be 3 different PRs?

[UebelAndre]

These are all things that I split out of #212 to try and make that more focused. I can split these commits up into different PRs if you prefer but I felt the changes were small enough that they could be bundled into one pull request.

[damienmg]

Sorry I realized I haven't answered. We squash all PR into a single commit so they make more sense as separate PR. It is a general approach at Google (and people using Gerrit) to do a code review per logical change (for this PR 1 change = 1 commit) and we tend to reflect this in our projects on github.

Do you mind splitting this into 3 PRs?

[UebelAndre]

@damienmg Sounds good and makes sense.

Done 😄
#213 #214

[damienmg]

Thanks!