H-227, H-229: Update Vault config and path construction

[CiaranMn]

🌟 What is the purpose of this PR?

This PR does the following:

• Updates the path construction for Vault secrets to avoid users of the Vault client attempting to use engines / paths we don't want used from the API (fixes H-229)
• Adds the Vault environment variables to the API Terraform config, ~and removes ROOT from the Vault token environment variable name, since we want to use a more specific token with a limited policy (being introduced to the Vault config in https://github.com/hashintel/internal-api/pull/133) – fixes H-227 once that linked PR is merged and we have created a token for that role for use in the API~ – we should use the iam auth method instead, see 'blocked by'
• Driveby: Removes a redundant environment variable for the Linear OAuth callback URL (it will never differ from ${apiOrigin}/oauth/linear/callback)
• Driveby: associates the user secret with the user always, and the integration with the owning workspace (rather than the user secret potentially being owned by an org as it was previously)

🚫 Blocked by

• [ ] https://github.com/hashintel/internal-api/pull/133 must be applied to create the Vault role for the API, ~which can then have a token created for it. Once the token is available we can merge this so that the API is deployed with it~
• [ ] implement the iam auth method with Vault (tokens have a time limit) and allow the API's execution role to use it – docs

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• [x] does not modify any publishable blocks or libraries, or modifications do not need publishing

📜 Does this require a change to the docs?

The changes in this PR:

• [x] are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• [x] do not affect the execution graph

❓ How to test this?

1. Check that creating a Linear integration still works

[linear[bot]]

H-229

H-227

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (211859a) 52.21% compared to head (75f15d8) 58.23%. Report is 1021 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2837      +/-   ##
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+ Coverage   52.21%   58.23%   +6.01%     
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  Files         337      240      -97     
  Lines       27987    25173    -2814     
  Branches      428       54     -374     
==========================================
+ Hits        14614    14659      +45     
+ Misses      13371    10508    -2863     
- Partials        2        6       +4     

Flag	Coverage Δ
backend-integration-tests	7.34% <ø> (ø)
unit-tests	18.36% <ø> (+18.36%)	:arrow_up:

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[CiaranMn]

Paths were updated in #4141 and environment variables added in #4174

There is still an outstanding task to use IAM profiles to connect to Vault (H-227).