Update tiltignore to enable auto-update yaml template in Tilt UI

[djdongjin]

What type of PR is this?
/kind bug

What this PR does / why we need it:
The .tilgignore causes that changes to yaml templates don't trigger re-execution of Tiltfile. Thus the Tilt UI cannot use updated templates.

This PR changes .tilgignore to include only subfolders under templates but not .yaml in the folder, so that Tilt can watch template files. Then if a yaml template is changed, Tilt will notice it and re-execute Tiltfile, thus the new template is used instead of the old one.

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #1766

Special notes for your reviewer:

Please confirm that if this PR changes any image versions, then that's the sole change this PR makes.

TODOs:

• squashed commits
• includes documentation
• adds unit tests

Release note:

NONE

[k8s-ci-robot]

Hi @djdongjin. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

I understand the commands that are listed here.

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[CecileRobertMichon]

/ok-to-test
/assign @mboersma @Jont828

[k8s-ci-robot]

@CecileRobertMichon: GitHub didn't allow me to assign the following users: Jont828.

Note that only kubernetes-sigs members, repo collaborators and people who have commented on this issue/PR can be assigned. Additionally, issues/PRs can only have 10 assignees at the same time.
For more information please see the contributor guide

In response to this:

/ok-to-test
/assign @mboersma @Jont828

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[mboersma]

Makes sense to me that this would help if you're changing the yaml templates locally.

Since .tiltignore honors .dockerignore syntax, here's another way to say "ignore everything under templates except yaml files in that directory":

templates
!templates/*.yaml

It's shorter and maybe a bit more future-proof, but slightly harder to understand. It's just a suggestion; this PR works as-is (I tested it).

[djdongjin]

@mboersma I agree that your version is more future-proof :). Updated with comments.

[mboersma]

/lgtm

The comments make it perfectly clear--thanks!

[CecileRobertMichon]

/lgtm
/approve

thanks @djdongjin!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: CecileRobertMichon

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [CecileRobertMichon]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[CecileRobertMichon]

/retest