"Image filename is accessible name for image" (9eb3f6): Add deprecated tag in title and metadata

[Jym77]

Deprecating the rule, as discussed during CG call on 14/01/2021.
See https://github.com/act-rules/act-rules.github.io/wiki/Minutes-2021-01-14#rules-ready-for-w3c-publication for discussion.

Deprecated tag is currently not handled in the website generation. See act-rules/act-rules-web#226

My idea here is to have the reason after the tag included in various parts of the website as needed.

Closes issue(s):

• N/A

Need for Final Call:
This will require a 2 weeks Final Call (deprecating a rule)

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[Jym77]

Final Call ends on February 3rd.

[Jym77]

Final Call has ended. Merging.