Configure default route timeout

Nobody has claimed this yet.

## Feature Request

### What problem are you trying to solve?
For routes configured in serviceprofiles without a timeout set the default is 10 seconds before the service returns a 504 to the requester. Lots of our routes take long to respond to some requests. It would be convenient for initial installation of serviceprofiles to optionally have a longer timeout, then tune the timeouts later.
### How should the problem be solved?
Allow for adding timeouts to all routes when creating a serviceprofile through `linkerd profile` or set the default timeout when performing `linkerd inject` or `linkerd install` or a helm chart option.
### Is there another way to solve this problem that isn't as good a solution?
Right now I use a sed script to add a default timeout to all routes after creating a serviceprofile. This works but is verbose and a potential gotcha for new folks who are confused why some of their routes return 504s after adding a new serviceprofile.
### How would users interact with this feature?
Possible cli options:
`linkerd profile --open-api "spec_file" --route-timeout=900s`
`linkerd install --route-timeout=900s`
`linkerd inject --route-timeout=900s`

docs:
https://linkerd.io/2/tasks/configuring-timeouts/

I am happy to submit an mr for this feature, but I don't know at what level this should be configurable.

Start by tracing the `linkerd profile`, `linkerd inject`, and `linkerd install` entry points and the Helm chart option handling; the issue does not name specific files or tests. Compare these configuration paths with the configuring-timeouts documentation and define where a route-timeout default should apply, then verify that the proposed CLI and chart options produce the intended route behavior.

Written by the indexing model from the issue text.