[generate_dump] Revert "Revert generate_dump optimization PR's #2599"…

…, add fixes for empty /dump forder and symbolic links (#2645)

- What I did
0ee19e5 Revert Revert the show-techsupport optimization PR's #2599
c8940ad Add a fix for the empty /dump folder inside the final tar archive generated by the show techsupport CLI command.
8a8668c Add a fix to not follow the symbolic links to avoid duplicate files inside the final tar archive generated by the show techsupport CLI command.

- How I did it
Modify the scripts/generate_dump script.

- How to verify it
1. Manual verification
do the show techsupport CLI command and save output original.tar.gz (with original generate_dump script)
do the show techsupport CLI command and save output fixes.tar.gz (with the generate_dump script modified by this PR)
unpack both archives original.tar.gz and fixes.tar.gz
compare both directories with ncdu & diff --brief --recursive original fixes Linux utilities
2. Run the community tests
sonic-mgmt/tests/show_techsupport

Signed-off-by: vadymhlushko-mlnx <vadymh@nvidia.com>