Cleanup backendmappings in history UI page

[raj-manvar]

Description

Currently the history.tsx which is for rendering the Query history page has backendMapping defined at https://github.com/trinodb/trino-gateway/blob/main/webapp/src/components/history.tsx#L18

It stores mapping between:
backend name -> backend proxy URL
backend proxy URL -> backend name
backend external Url -> backend name.

From usage, only the ProxyUrl -> backend Name mapping is used while displaying the backend name in the list of query history, rest mapping can be cleaned up.

Additional context and related issues

Release notes

(x) This is not user-visible or is docs only, and no release notes are required.
( ) Release notes are required, with the following suggested text:

[andythsu]

For UI change, could you include a picture of before and after so it's clear on what the changes are?

[raj-manvar]

Yes Thanks, I can include this. Though, for this change we dont expect any UI changes, it's mostly just code cleanup. I'll add the UI screenshot after running the branch locally

[RoeyoOgen]

@raj-manvar any update?

[raj-manvar]

[raj-manvar]

[raj-manvar]

[raj-manvar]

[raj-manvar]

Sorry @RoeyoOgen for the delay. Added screenshot and also rebased with latest main branch

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Raj Manvar.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email [email protected]
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails