Elastic Agent `--include servers` install option + updated binary size

[kilfoyle]

From Nima's comment:

For 9.0:

• We will calculate a new set of agent binary size.
• The main change is elastic-agent install -install-servers command option. Users pre-9.0 didn't have to do this when installing the Fleet-server and now they will have to. It affects cloudbeat, apm-server, fleet-server users.

[nimarezainia]

@kilfoyle the command is --install-servers rather than --include-servers. I changed the description. (during the development process this command was changed)

[kilfoyle]

I think this can be closed now. The --install-servers option is included as part of the "Document Agent Install Flavors" PR: elastic/docs-content#927

[kilfoyle]

Actually... we still need to update the binary sizes for 9.0.

[kilfoyle]

Updated binary sizes will be added by:

• 9.0 docs: [Fleet] Add Elastic Agent binary sizes docs-content#1251
• 8.19 and 8.18 docs: Update Elastic Agent binary sizes #1777