Add minimal resource requests for tgi

[yongfengdu]

Description

This is the first PR for #643 , the plan is to get tgi change reviewed and merged, then doing the same for other charts.(To avoid too many CI testing)
Tried several requests settings(With small values) and it doesn't have obvious impact on the resource usage.
So set this should be good enough.
cpu: 100m
memory: 128Mi

It's performance tuning's task to set more reasonable resource limit/requests according to different scenarios.

Issues

#643

Type of change

List the type of change like below. Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would break existing design and interface)

Dependencies

List the newly introduced 3rd party dependency if exists.

Tests

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[lianhao]

Let's have this as a starter and put more meaningful values once the opea SLA is defined.