Generation support for 1.10 - build dev 1.10 pr16

[sdavtaker]

• Issue #1888 *

Description of changes:

• Updating Generator Java code
• Adding message about REGENERATE_CLIENT removal
• Refactor generate_sdks.py
• Updating Generator templates for 1.10

This change doesn't include regeneration of all clients, only DDB, neither the inclussion of all of them at the generated directory level. Holding that for follow up PR since will create a lot of noise here.

Check all that applies:

• [x] Did a review by yourself.
• [ ] Added proper tests to cover this PR. (If tests are not applicable, explain.)
• [ ] Checked if this PR is a breaking (APIs have been changed) change.
• [ ] Checked if this PR will not introduce cross-platform inconsistent behavior.
• [ ] Checked if this PR would require a ReadMe/Wiki update.

Check which platforms you have built SDK on to verify the correctness of this PR.

• [ ] Linux
• [ ] Windows
• [ ] Android
• [ ] MacOS
• [ ] IOS
• [ ] Other Platforms

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