Rename 'spring.http.client' properties to 'spring.http.client.settings'

[philwebb]

Much like we have properties.actuator.management.endpoints for properties that change all endpoints, we should have probably really named spring.http.client as spring.http.clients.

EDIT: We've reconsidered and we'd like to use spring.http.client.settings

[shivammm21]

I've implemented the requested changes to rename the properties from 'spring.http.client' to 'spring.http.clients' as suggested in issue #44958.

I've fixed the DCO sign-off issue and am willing to make any additional changes if needed.

[philwebb]

Thanks @shivammm21 but I'm already working on this one. I'd suggest checking the 'Assignees' and labels before submitting any pull-requests.

[shivammm21]

Yeah, I am sorry. First, I will comment on it to assign me after I am assigned, and then I will create pr.