Fix #1253 - upgrade to bootstrap 5.0.1 stable.

[farmakiG]

Changes in this Pull Request:

• Upgraded bootstrap 5.0 beta 3 to bootstrap 5.0.1 stable.
• Tested if Logout, Dropdowns, popovers etc. still work. Please see here what has been changed in v5.

Mandatory checks:

• [X] Branch is up to date (latest changes were fetched from the upstream branch before creating this PR)
• [X] Changes were tested manually
• [ ] Java code changes are unit tested
• [ ] Webtests are successful

To be checked by the reviewer:

• [ ] Clean Java code and unit tested changes
• [ ] UI customizablity is preserved: No hard-coded styling and URL references in JSF views

To be checked by the pull request owner:

• [ ] .MASTER/job/BES_MASTER_IT/
• [ ] .MASTER/job/OSCM_WS_Tests_INTERNAL/
• [ ] .MASTER/job/OSCM_WS_Tests_OIDC/
• [ ] .MASTER/job/OSCM_Integration_Tests_INTERNAL/
• [ ] .MASTER/job/OSCM_Integration_Tests_OIDC/

Cross repository and core changes:

• [ ] Interdependent changes have been communicated to the team (if applicable)
• [ ] This pull request includes high risk modifications or core changes (e.g API, datamodel, authentication...). Mandatory reviewers: @goebell or @kowalczyka.

OSCM Build References:

• est6

Screenshot (if applicable):

• add a screenshot illustrating your change

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This change is 

[codecov[bot]]

Codecov Report

Merging #1255 (36d1c63) into master (251bdf0) will not change coverage. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #1255   +/-   ##
=========================================
  Coverage     55.47%   55.47%           
  Complexity    14427    14427           
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  Files          1375     1375           
  Lines         80473    80473           
  Branches       8598     8598           
=========================================
  Hits          44643    44643           
  Misses        33140    33140           
  Partials       2690     2690