_cat/threadpool remove "size" and add "time" params

[jakelandis]

The rest spec and documentation for _cat/threadpool supports a "size" parameter.
However, the "size" parameter will have no impact since there are no values
of type "SizeValue" of the return value of this _cat api.

This commit removes the "size" param from the spec and documentation.

This commit also adds support for the "time" param since and support to
format the time param for the "keep_alive" column. By default, the output
should not change since the "TimeValue" rendered default (via RestTable)
is toString(), and the code prior to this also called toString().

closes #54478

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/CAT APIs)

[russcam]

LGTM.

Client generators may use the params in REST specs to generate methods/members/types for the allowed parameters for an API. For example

• the .NET client generates a Size enum and a Size? property on CatThreadPoolRequestParameters
• the Rust client generates a Size enum and a size() fn on CatThreadPool<'a, 'b>
• The go client generates a Size member on CatThreadPoolRequest

Because of this, I don't believe this change should be backported to 7.x, since it would result in removing these types and members within a major version in clients.

/cc @elastic/es-clients

[Mpdreamz]

In the 7.x branches these parameters can be documented as deprecated and the description could read that these parameters are effectively a noop or rejected by the server.

[jakelandis]

In the 7.x branches these parameters can be documented as deprecated and the description could read that these parameters are effectively a noop or rejected by the server.

Will do, and will hold up this issue until that is done. (trying to ensure changes go through master first)

[jakelandis]

Removed the 7.x labels and will only merge this to 8.x. I am not adding the >breaking label because this is not technically breaking in ES. Clients (previous to this PR) that sent the "size" param will continue to work as it always did which has no impact on the result. (all the cat APIs support a common set of params and sometimes they are not applicable)

[jakelandis]

blocked by #55984

[jakelandis]

@elasticmachine run elasticsearch-ci/bwc
@elasticmachine run elasticsearch-ci/default-distro

[jakelandis]

@elasticmachine update branch

[jakelandis]

@elasticmachine update branch