_Context:_
Normally, all open issues/PRs in the repository that's running this
action are retrieved then all the label, assignee, milestone, etc. criteria
you provide to the action are applied. Unfortunately, this limits the action
to only those issues and PRs in this repository.  It also prevents operating
on only a subset of issues or PRs that can't be filtered by the existing
action criteria.  A good example of this are PRs that are in a
`review:changes_requested` state.  While additional filtering criteria could
be added to the action, it would result in additional callbacks to GitHub
which could trigger rate-limits to be applied.

_Purpose:_
This option is an array of one or more standard [GitHub Issues and
Pull Requests search queries]
(https://docs.github.com/en/search-github/searching-on-github/searching-issues-and-pull-requests)
which will be used to retrieve the set of issues/PRs to test and take action
on. These queries will be used in place of the default retrieval of all open
issues and PRs for the context's owner/repo.  It can be used to expand or
limit the set of issues and PRs operated on beyond what is retuned by the
standard query.  When the retrieval is complete, all the other label,
assignee, milestone, etc. criteria will be applied.

You may also use this option to improve performance when you have a large number
of open issues or PRs but only a small subset might be eligible for action. For
instance, let's say you have 1000 open issues in your repository but only those
with label `auto-closable` should ever be automatically marked as stale or
closed.  By default, this action would retrieve all 1000 issues _and all open
PRs_ and iterate over them looking for the label you specified in the
`only-issues-label` parameter. If you use the `only-matching-filter` parameter
with `repo:myorg/myrepo is:issue label:auto-closable` this would limit the
download to just those issues you  _know_ should  have further criteria
applied.

_Syntax:_

```
only-matching-filter: [ "<query_string>", ... ]
```

Or if there's only one query string...

```
only-matching-filter: '<query_string>'
```

_Examples:_
To operate only on the open PRs in your organization that have a review state of
`changes_requested`:

```
only-matching-filter: 'org:myorg is:pr is:open review:changes_requested'
```

Since there's only one query specified, you can omit the array syntax and just
specify the string directly.

GitHub only allows boolean logic and grouping in a Code Searches not in Issues
and Pull Requests searches so there's no way to do an "OR" operation but you
can get around this to a limited degree by specifying multiple search queries
in the form of a string array. Each query is run separately and the results are
accumulated and duplicates removed before any further processing is done.

To retrieve all of the open PRs in your organization that have a review state of
`changes_requested` or a label named `submitter-action-required`, you'd use:

```
only-matching-filter: '[ "org:myorg is:pr is:open review:changes_requested", "org:myorg is:pr is:open label:submitter-action-required" ]'
```

_Notes:_
* Each query is checked to ensure it contains an `owner:`, `org:`, `user:` or
`repo:` search term.  If it doesn't, the search will automatically be scoped
to the owner and repository in the context to prevent accidental global
searches.  If the request doesn't already contain an `is:open` search term,
it will automatically be added as well.
* If using the array form, the value of this parameter MUST be valid JSON
which means using double quotes around each query string, not single quotes.

Default value: '[]'

Resolves: actions#1143