We've settled on the nomenclature `upstream-repo` to refer to the
original repository of the project, as opposed to the `pr-repo` which is
a fork that exists exclusively to let GitGitGadget handle PRs in (and to
store its global state in the Git notes). So let's call the owner of the
`upstream-repo` the `upstreamOwner`, not the `baseOwner`.

Besides, with GitHub's naming conventions referring to the branch a PR
targets as the "base", it is a bit confusing to have `baseOwner` to
refer to anything except the owner of the repository in which the PR
lives.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

The `owners` array refers to a list of orgs/owners where the GitHub App
is installed, i.e. where GitGitGadget can operate.

Therefore, a much better place is `app.installedOn`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

The idea is to configure GitGitGadget via a `gitgitgadget-config.json`
file that contains the project-specific instance of the `IConfig`
interface, tracked in the `config` branch of a fork of the
`gitgitgadget-workflows` repository, from where it is automatically
synchronized via a GitHub workflow to the repository variable `CONFIG`,
and then passed to all of GitGitGadget's Actions via:

	```yml
	config: '${{ vars.CONFIG }}'
	```

For now, this input is optional, to ease the transition of GitGitGadget;
Eventually, this config will be required, so that several projects can
be served using identical source code in forks of the
`gitgitgadget-github-app` and `gitgitgadget-workflows` repositories.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

GitGitGadget now accepts the project configuration as a `config` Action
input, in the form of a string that contains the JSON-encoded `IConfig`
object. That is a bit fragile, though, as it is all-too-easy to have a
typo in that object.

Let's install `typia` to use the `IConfig` interface as a source of
truth when validating the user input.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

This uses the freshly-installed `typia` module to create a validator for
the `IConfig` interface at compile-time, and uses it to validate
user-provided JSON against that interface.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

For the `typia`-based validator, it is good to label each and every
attribute's type so that the error messages are helpful.

This commit is best viewed with `--ignore-space-change`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

This way, the maximal number of columns can be configured freely per
project, via the project-specific config.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Currently this URL is constructed from the `host` and the `name`
attributes of the project config setting's `mailrepo` attribute.

However, the `name` is supposed to refer to the mailing list _mirror
repository_, while we are interested in the URL where the web UI of the
public-inbox instance lives. Luckily, we already have that in the
project configuration: It's the `url` attribute.

I noticed the need for this patch in
cygwingitgadget/cygwin#1, where the URL
displayed after submitting v1 pointed to an incorrect location.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

This will come in handy once the project-specific settings start living
in the `config` branch.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>