Add deprecated tags in preparation for release 8.0.0

Summary

Add the deprecated tag to some applications, classes and function, mainly in preparation of the OSSIM removal.

Rationale

To remove applications, classes and function in the release 8.0, we need to deprecate them in the previous release.

Implementation Details

Classes and files

• OssimAdapters classes

Applications

• DownloadSRTMTiles (see #2164 (closed))

Functions

• otb::ImageKeywordList accessors are deprecated in favor of otb::Metadata accessor

Copyright

The copyright owner is CNES and has signed the ORFEO ToolBox Contributor License Agreement.

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Check before merging:

• All discussions are resolved
• At least 2 votes from core developers, no vote.
• The feature branch is (reasonably) up-to-date with the base branch
• Dashboard is green
• Copyright owner has signed the ORFEO ToolBox Contributor License Agreement
• Optionally, run git diff develop... -U0 --no-color | clang-format-diff.py -p1 -i on latest changes and commit