Allow automatic rotation of linkerd-trust-anchor CA

Nobody has claimed this yet.

### What problem are you trying to solve?

I'm trying to fully automate certificate management with cert-manager following this helpful guide by @mateiidavid : https://github.com/linkerd/linkerd2/issues/7345#issuecomment-979207861

In this case, `linkerd-trust-anchor` CA is created by cert-manager and it's public certificate is distributed using trust-manager's bundle into `linkerd-identity-trust-roots` configmap.

Everything works as expected as far as I can tell.

However, when `linkerd-trust-anchor` CA is rotated, and trust-manager distributes new `linkerd-identity-trust-roots` bundle, it doesn't look like linkerd picks it up.

It looks like I have to reload both linkerd control plane services, and all cluster workloads to pick up the new `linkerd-identity-trust-roots`.

### How should the problem be solved?

I wonder if it would be possible to monitor changes in `linkerd-identity-trust-roots` config map and pick up new trusted bundle automatically?

Also, for workloads (linkerd-proxy), it looks like trust roots are picked up at start and can only be re-read by restarting the workloads. I wonder if they could query new bundle automatically too?

Please, correct me if I'm wrong in my assumptions here.

### Any alternatives you've considered?

If understand correctly, there are two alternatives here:

- Generate original CA with a very long duration time (e.g. 10 years) to it doesn't get rotated by cert-manager
- Monitor `linkerd-trust-anchor` rotation and restart both linkerd control plane services and all workloads

### How would users interact with this feature?

_No response_

### Would you like to work on this feature?

None

Start by investigating how the linkerd-identity-trust-roots ConfigMap is consumed by Linkerd control plane services and linkerd-proxy, and whether it is watched or only read at startup. Verify the behavior when cert-manager and trust-manager rotate the CA, then define tests for updating trust roots without restarting services or workloads.

Written by the indexing model from the issue text.