FR: sort matchers on silences page

[rc5hack]

Currently matchers are not sorted on "silences" page. I ask to add sorting.

What did you do?
Create 2 silences with matchers:

1. instance=foo job=myjob alertname=InstanceDown
2. alertname=InstanceDown instance=bar job=myjob

Go to alertmanager silences page.

What did you expect to see?
Sorted matchers, like this:

1. alertname=InstanceDown instance=foo job=myjob
2. alertname=InstanceDown instance=bar job=myjob

What did you see instead? Under which circumstances?
Unsorted matchers:

1. instance=foo job=myjob alertname=InstanceDown
2. alertname=InstanceDown instance=bar job=myjob

Environment

• Alertmanager version:
  0.27.0 (0aa3c2a)

• Prometheus version:
  2.51.2 (b4c0ab52c3e9b940ab803581ddae9b3d9a452337)

[grobinson-grafana]

@rc5hack sounds fine to me! Can you open a PR for this?