[hotfix][docs] add Back to top button

[leesf]

What is the purpose of the change

Add back to top button for connectors overview docs.

Brief change log

Add back to top button for connectors overview docs.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[lamberken]

hi, @leesf , happy new year. thanks for your pr. I think it's better to check all docs which need add back to top button.
for example, java_lambdas, ml, broadcast_state doc, and etc

[lamberken]

happy new year 🎉

hi, @zentol. maybe it's better these java_lambdas, ml, broadcast_state doc need to add back to top button. do you think so? if so, it's no need to open a new pr

Best, lamber-ken

[leesf]

@lamber-ken happy new year, thanks for your reviewing. I could check all docs without Back to top button and update my another pr (#7360) since this pr is merged. cc @zentol

[lamberken]

@lamber-ken happy new year, thanks for your reviewing. I could check all docs without Back to top button and update my another pr (#7360) since this pr is merged. cc @zentol

👍