docs: add instructions for setting Studio version label to custom studio images

[georgi-seqera]

Summary:

Updating instructions for custom studio creation steps to include adding a image label io.seqera.connect.version to identify the connect-client version used based on image label metadata.

Note: This change is not tied to any release as it is purely widely supported Docker functionality and hence can be applied to docs at any time and even can be applied to older enteprise version documentation.

Context:

Certain studio functionalities require the Seqera Platform to know the version of the connect-client used at the point of configuring and launching the studio.

To do this effectively, all custom built studio images must have a io.seqera.connect.version label with the connect-client version used going forward.
While the absence of the label will not block a studio being started (and will work as before), it might not support all new functionalities (e.g. ssh connectivity).

Related updates:

• The custom-studios-examples repository is being updated with the same change to reflect the documentation
  • feat: add connect-client version label to images custom-studios-examples#16
• Additionally we'd perhaps want to update blog post for custom studios to also reflect this additional step as the blog post is widely referenced and useful
  • https://seqera.io/blog/deploy-custom-apps-studios/

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