Update images for the new releases on Q4`20

[avtikhon]

gitlab-ci: update tags/branches and bump versions

Added new tags with manual builds:
1.10.9: 1.10.9-0-g720ffdd23
2.5.3: 2.5.3-0-gf93e48013
2.6.2: 2.6.2-0-g34d504d7d
2.7.1: 2.7.1-0-g3ac498c9f
2.8.0: 2.8.0-0-gefc30ccf8

Bumped branches:
2.5: 2.5.3-0-gf93e48013
2.6: 2.6.2-0-g34d504d7d
2.7: 2.7.1-0-g3ac498c9f

Updated stable images:
*1.x: 1.10.9-0-g720ffdd23
*2.x: 2.6.2-0-g34d504d7d