Fix Gremlin Server 3.7

[kmcginnes]

Graph Explorer breaks in Gremlin Server 3.7 because the response content type changed from 3.6.

To ensure we always get the content type we expect we set the header:

"Accept": "application/vnd.gremlin-v3.0+json"

This is done on the client and the server.

Validation

• Test with Gremlin Server 3.6
• Test with Gremlin Server 3.7
• Test with Neptune 1.3

Related Issues

• Fixes #277

Check List

• [x] I confirm that my contribution is made under the terms of the Apache 2.0 license.
• [x] I have run pnpm checks to ensure code compiles and meets standards.
• [x] I have run pnpm test to check if all tests are passing.
• [ ] I have covered new added functionality with unit tests if necessary.
• [x] I have added an entry in the Changelog.md.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 14.94%. Comparing base (361c4ba) to head (8ae0601). Report is 20 commits behind head on main.

Files	Patch %	Lines
...-explorer/src/connector/gremlin/gremlinExplorer.ts	0.00%	7 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #411 +/- ## ========================================== + Coverage 13.97% 14.94% +0.96% ========================================== Files 414 415 +1 Lines 30639 30809 +170 Branches 878 953 +75 ========================================== + Hits 4283 4604 +321 + Misses 26026 25878 -148 + Partials 330 327 -3 ``` | [Flag](https://app.codecov.io/gh/aws/graph-explorer/pull/411/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aws) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/aws/graph-explorer/pull/411/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aws) | `14.94% <0.00%> (+0.96%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=aws#carryforward-flags-in-the-pull-request-comment) to find out more.

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