clarify https not suported, artifact versions not immutable, add openapi example

[smccarthy-ie]

Update RHOSR Getting Started as follows:

• Clarify HTTPS not supported when uploading artifacts (customer request)
• Clarify artifact versions no longer immutable (can be deleted using REST API)
• Add example of uploading artifact using URL (and update screenshot)
• Make more generic to fit API and schema use cases

[bredamc]

Some additional minor comments (can't append comments to the relevant lines in the Files changed tab) -- the line numbers below refer to the position in the edited file, not the original position.

1. General: Should we include a link to the "web console" in step 1 of each section (similar to the link in step 1 of the "Creating a Service Registry instance" section)?
2. Figure 1 should be updated to show that the heading now includes the word Instances: "Service Registry Instances"
3. Line 249: Change "chose" to "choose"?
4. Line 251: Change "... the most powerful and ..." to "... the most powerful API and ..."?
5. Lines 251-253: Append a fullstop to each bullet point?
6. Line 255: Move the second sentence to a new line, and change "This is the server endpoint that you’ll need to connect ..." to "You’ll need this server endpoint to connect ..."
7. Line 274: Move the second sentence to a new line, and change " This is the endpoint that you’ll use with your service account credentials to authenticate ..." to "You’ll use this endpoint with your service account credentials to authenticate ..."

[smccarthy-ie]

Thanks for the great feedback Breda. Ready for re-review/approval.