[bukuserver] Bookmark update error message

[LeXofLeviafan]

fixes #646:

• moving success logic on save (caching saved ID in session dict or raising an error on failure) out into a separate method
• using said method in both create and update handlers to handle save logic
  note: flask-admin handles edit errors differently in debug and production mode

[rachmadaniHaryono]

as note this is test list i made for bukuserver

• bookmarklet
  • test new url
    • test without any input
      • fetch
      • no fetch
    • test with selected text
  • test url already in db
• bookmark
  • create
    • url only
    • fetch
    • no fetch
    • description
    • title
    • tag
  • delete
  • update
    • any
    • change url to another existing url
  • filter
• tag
  • update
  • delete
  • filter
• statistic
  • filter
    • netloc
    • tag
    • title

some issue fixed on #643 also tested using above test list

[LeXofLeviafan]

as note this is test list i made for bukuserver

I'm guessing you'll be adding this in a separate pull-request?

[jarun]

@rachmadaniHaryono @LeXofLeviafan can this be merged?

[rachmadaniHaryono]

@jarun yes

e:

I'm guessing you'll be adding this in a separate pull-request?

yes @LeXofLeviafan , maybe here https://github.com/jarun/buku/wiki/PR-guidelines for now

[jarun]

Thank you!

[jarun]

@LeXofLeviafan CI is failing. Please check.

[rachmadaniHaryono]

CI is failing. Please check.

as stated here https://github.com/orgs/Buku-dev/teams/dev/discussions/2/comments/7 i will take care of it