Previously, the tweet tasks fetched Twitter API credentials implicitly
from the environment, and a dryRun bool parameter was used to disable
the task from actually posting a tweet (useful for running tests).

This doesn't scale well to being able to supply different credentials,
which is needed to be able to run the task in a staging environment,
using a staging/test set of credentials.

Create an ExternalConfig struct for providing secrets for external
services that tasks need to interact with, making this more explicit.

This will be used by relui in its upcoming "create tweet" workflows.

Update the MailDLCL task analogously to accept the new ExternalConfig
parameter, making it more testable and dry-run-capable in the process.

Also switch to using *workflow.TaskContext (pointer, not value),
since that's what the x/build/internal/workflow package expects.

For golang/go#47402.
Updates golang/go#47405.

Change-Id: I40f0144a57ca0031840fbd1303ab56ac3fefc6c6
Reviewed-on: https://go-review.googlesource.com/c/build/+/382935
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

Previously, it was only possible to create workflow parameters
with the implicit "string" type hard-coded. Some workflows we're
creating either require or will benefit from more flexibility
in parameter types (slices of strings, single-line vs multi-line
strings, and so on). It was also not yet possible to associate
metadata to parameters (such as documentation, example values).

This change implements that flexibility for workflow parameters,
and uses it to better document the existing Twitter workflows.
The next change will add a workflow that uses new slice types.

For simplicity and clarity reasons, all parameter information
is contained in one place in the workflow.Parameter struct,
including some fields that control the HTML presentation of
said parameters, instead of trying to factor out HTML bits
into the relui package and creating a bridge between the two.

Also type check in more stages of the workflow processing.

For golang/go#47405.
Fixes golang/go#51191.

Change-Id: Ia805b3b355e65fcbf2397ad21800da448ccb826a
Reviewed-on: https://go-review.googlesource.com/c/build/+/404454
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
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This CL contains just the templates and test data for review
convenience. The next CL in the stack holds the implementation.

The email templates have a MIME-style header with a Subject key,
which is used to determine the email subject, and the rest is
the email body in Markdown format.

While the announcement emails have been generated from templates
for a while, there was variation in minor formatting and wording
over the years. These templates are converted to Markdown and
attempt to not to deviate from the average past announcements
too much while correcting minor inconsistencies.

Making larger changes can be considered later. It should be easier
now that this task is driven by templates without outsourcing the
responsibility of HTML formatting and editing to the human senders.

For golang/go#47405.
Fixes golang/go#47404.

Change-Id: Ie04d94b35ce1b5d111eeb1b0b076c034ba3f4dcb
Reviewed-on: https://go-review.googlesource.com/c/build/+/412754
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

I don't know why I added commas, maybe thinking of JSON,
but they cause a YAML parse error so we can't keep them.

Also get rid of a misplaced word in a log message.

For golang/go#47405.

Change-Id: I1072a4c4f563704345100620c5e1fdfdf7df3dcd
Reviewed-on: https://go-review.googlesource.com/c/build/+/413074
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Alex Rakoczy <alex@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>