Implement envManagement args for `::writeManifest()`

[dbkegley]

Closes #977

Adds the following args for all commands that write bundle manifests

• envManagement
• envManagementR
• envManagementPy

QA:

# writes a manifest with environment.environment_management.r and environment.environment_management.python = false
rsconnect::writeManifest(..., envManagement=FALSE)

# writes a manifest with environment.environment_management.r and environment.environment_management.python = true
rsconnect::writeManifest(..., envManagement=TRUE)

# writes a manifest with environment.environment_management.r = true
# environment.environment_management.python is not defined
rsconnect::writeManifest(..., envManagementR=TRUE)

# writes a manifest with environment.environment_management.python = true
# environment.environment_management.r is not defined
rsconnect::writeManifest(..., envManagementPy=TRUE)

# writes a manifest with environment.image = "my/image:latest"
# environment.environment_management is not defined
rsconnect::writeManifest(..., image="my/image:latest")

[ChaitaC]

Verified on branch

RemoteSha: 382e35b0e265b8c23314cef7fe4384267f96a9f5
GithubRepo: rsconnect
GithubUsername: rstudio
GithubRef: kegs-env-management

• [x] devtools::install_github("rstudio/rsconnect","kegs-env-management")

• [x] writes a manifest with environment.environment_management.r and environment.environment_management.python = false

  rsconnect::writeManifest(..., envManagement=FALSE)

  

• [x] writes a manifest with environment.environment_management.r and environment.environment_management.python = true

  rsconnect::writeManifest(..., envManagement=TRUE)

  

• [x] writes a manifest with environment.environment_management.r = true

• [x] environment.environment_management.python is not defined

  rsconnect::writeManifest(..., envManagementR=TRUE)

  

• [x] writes a manifest with environment.environment_management.python = true

• [x] environment.environment_management.r is not defined

  rsconnect::writeManifest(..., envManagementPy=TRUE)

  

• [x] writes a manifest with environment.image = "my/image:latest"

• [x] environment.environment_management is not defined

  rsconnect::writeManifest(..., image="my/image:latest")

  

[ChaitaC]

@dbkegley minor nit: envMangementR and envManagementPy does not say Posit Connect vs envManagement description says Posit Connect