Optimize `sources.sh`

[mkurz]

It should not be necessary to list all files manually.

See comments in

• Publish sources of examples as separated artifacts are attached to pre-release #569

TODO:

• main branch
• 3.0.x branch
• 2.9.x branch

[ihostage]

Also need to think about good name for release/tag for main branch.
See #569 (comment)

[mohdshubair313]

can I contribute on this . How can I help you

[ihostage]

Hi, @mohdshubair313!
I think this issue will be actual only after #558

[ihostage]

@mohdshubair313 this issue is ready to work if you still interested 😉