Add Hosting Block Convenience Method to SDK

[emma-steuer]

Related Issue(s):

Closes #

Proposed Changes:

For inclusion in changelog (if applicable):

1. Support Subscriptions API hosting block for Sentinel Hub in the CLI (Add Hosting Block Convenience Method to SDK #1029).

Not intended for changelog:

1. N/A

Diff of User Interface

Old behavior: Hosting was not supported for create and request for the Subscriptions CLI.

New behavior: Hosting is now supported for both create and request in the Subscriptions CLI. --hosting and --collection_id are flags used for this.

PR Checklist:

• This PR is as small and focused as possible
• If this PR includes proposed changes for inclusion in the changelog, the title of this PR summarizes those changes and is ready for inclusion in the Changelog.
• I have updated docstrings for function changes and docs in the 'docs' folder for user interface / behavior changes
• This PR does not break any examples or I have updated them

(Optional) @mentions for Notifications:

[asonnenschein]

Following up re: other places in the CLI where the hosting flags could be added --

The CLI has convenience methods that structure JSON payloads from flagged arguments (see https://planet-sdk-for-python-v2.readthedocs.io/en/latest/cli/cli-subscriptions/#subscription-request-conveniences). JSON output from these commands can be piped into the subscriptions create command. With that in mind, I think convenience method request (https://github.com/planetlabs/planet-client-python/blob/main/planet/cli/subscriptions.py#L274) should be enhanced with hosting flag arguments similar to the create command.

[asonnenschein]

LGTM! Could you please fill out the MR description before merging?